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The Gulf of St. Lawrence Is closed to commercial navigation for nearly five months each year due to ice conditions. In order to lengthen the shipping season, greater knowledge of the behaviour of the ice is necessary. A step in this direction was the inauguration in 1940 of aerial ice surveys in the gulf during the breakup season. The surveys have continued annually for the past thirteen years.
Based primarily on the data provided by these surveys, maps were drawn showing the limits of the main ice areas in each breakup season. Although the maps enabled the isolation of several distinct patterns and rates of breakup, they revealed that the behaviour of the ice was extremely variable. The factors influencing ice conditions, including tides, ocean currents, temperature, and wind, were examined with the aim of discovering the causes of the breakup patterns. A number of factors were found to be important in determining the fundamental behaviour of the ice, bat the meteorological factors of temperature and wind appeared to be the chief agents in causing the variable behaviour from year to year.
In spite of these variations, it was possible to trace average conditions throughout the Ice season. The chief characteristics of the ice season may be stated briefly. The Gulf of St. Lawrence is never completely covered with ice, but rather, it is partly covered with fields of shifting pack ice between which lie broad stretches of open water. The southern part of the gulf is an area of accumulation where ice conditions are most serious. The clearing of ice from the gulf begins slowly in January and February and becomes accelerated in March and April. The bulk of the ice moves through Cabot Strait to the open Atlantic rather than remaining inside the gulf until it melts. Generally, the ice either withdraws from west to east, passing through Cabot Strait directly, or it stagnates in the southern part of the gulf toward the end of the season. By the first of May the gulf is usually clear of ice which constitutes a hinderance to navigation.

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ICE DISTRIBUTION IN THE GULP OF ST. LAWRENCE DURING THE BREAKUP SEASON by CHARLES NELSON FORWARD A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS In the Department of Geology and Geography We accept t h i s thesis as conforming to the standard required from candidates f o r the degree of MASTER OF ARTS. Members of the Department of THE UNIVERSITY OF BRITISH COLUMBIA September, 1952 ICE DISTRIBUTION IN THE GULP OF ST. LAWRENCE DURING THE BREAKUP SEASON toy CHARLES NELSON FORWARD AN ABSTRACT OF A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS i n the Department of Geology and Geography THE UNIVERSITY OF BRITISH COLUMBIA September, I952 2 The G u l f of S t . Lawrence Is c losed to commercial n a v i g a t i o n f o r nearly f i v e months each year due to i c e c o n d i t i o n s . In order to lengthen the shipping season, greater knowledge of the behaviour of the i c e i s necessary. A step i n t h i s d i r e c t i o n was the inauguration i n 1$HQ of a e r i a l i c e surveys i n the g u l f during the breakup season. The surveys have continued annually f o r the past t h i r t e e n y e a r s . Based p r i m a r i l y on the data provided by these surveys, maps were drawn showing the l i m i t s of the main i c e areas i n each breakup season. Although the maps enabled the i s o l a t i o n of s e v e r a l d i s t i n c t patterns and rates of breakup, they revealed that the behaviour of the i c e was extremely v a r i a b l e . The f a c t o r s i n f l u e n c i n g i c e c o n d i t i o n s , i n c l u d i n g t i d e s , ocean c u r r e n t s , temperature, and wind, were examined with the aim o f d i s c o v e r i n g the causes of the breakup p a t t e r n s . A number of f a c t o r s were found to be important In determining the fundamental behaviour of the i c e , bat the meteorological f a c t o r s of temperature and wind appeared to be the c h i e f agents i n causing the v a r i a b l e behaviour from year to y e a r . In s p i t e of these v a r i a t i o n s , I t was"possible to trace average c o n d i t i o n s throughout the Ice season. The c h i e f c h a r a c t e r i s t i c s of the i c e season may he stated b r i e f l y . The Gulf of S t . Lawrence i s never completely covered with i c e , but r a t h e r , i t i s p a r t l y covered w i t h f i e l d s of s h i f t i n g pack i c e between which l i e broad stretches of open water. The southern part of the g u l f i s an area of accumulation where i c e c o n d i t i o n s are most s e r i o u s . The c l e a r i n g of ice from the gulf begins slowly in January and February and becomes accelerated in March and April. The bulk of the ice moves through Cabot Strait to the open Atlantic rather than remaining inside the gulf until i t melts. Generally, the ice either withdraws from west to east, passing through Cabot Strait directly, or i t stagnates in the southern part of the gulf toward the end of the season. By the first of May the gulf is usually clear of ice which constitutes a hinderance to navigation. TABLE OF CONTENTS CHAPTER I INTRODUCTION The problem Sources of information Procedures Terminology Organization II PHYSICAL GEOGRAPHY Subaerial and submarine morphology Water movements and propert ies Tide8 and t i d a l currents Ocean currents Phys ica l propert ies Climate Temperature P r e c i p i t a t i o n Wind Summary III WINTER ICE CONDITIONS December January February Summary IV ICE DISTRIBUTION IN THE BREAKUP SEASON DURING THE YEARS I94O-I952 INCLUSIVE Season of 19*W Season of I9UM Season of 19^2 Season of 19*1-3 Season of I9U4 Season of Season of 19^6 Season of I9U7 Season of 19^ -g Season of 19^9 Season of I95O Season of I95I Season of 1952 CHAPTER V THE NATURE GP THE BREAKUP AND THE DETERMINING FACTORS Patterns and rates of breakup The determining factors of the breakup The non-variable factors Subaerial and submarine morphology Tides and t i d a l currents Ocean currents Variable factors Physical properties of the water Meteorological factors Temperature P r e c i p i t a t i o n Wind Summary VI CONCLUSION BIBLIOGRAPHY APPENDIX LIST OF TABLES TABLE PAGE I Monthly Averages of Dally Mean Temperature 26 I I R e l a t i o n s h i p s Between Temperature, Wind, and Ice Conditions V LIST OF MAPS HAP FOLLOWING? PAGE 1 Gulf of S t . Lawrence: Place Names 14- 2 Submarine Contours 15 3 T i d a l Ranges 1 § 4 Ocean Currents 21 5 Isotherms of Mean Monthly Temperature 25 b Percentage Frequency of Wind 27 7 Average Date of C l o s i n g of Harbour Navigation 32 S Locations of M e t e o r o l o g i c a l S t a t i o n s 40 9 Limit8 of Main Ice Areas, Season of 1940 Appendix 10 L i m i t s of Main Ice Areas, Season of 194-1 tt 11 L i m i t s of Main Ice Areas, Season of 1942 " 12 L i m i t s of Main Ice Areas, Season of 194-3 " 13 L i m i t s of Main Ice Areas, Season of 1944 " 14 L i m i t s of Main Ice Areas, Season of 1§45 • 15 L i m i t s of Main lee Areas, Season of 1946 B 16 L i m i t s of Main Ice Areas, Season of l§4-7 " 17 L i m i t s of Main Ice Areas, Season of 1946 " IS L i m i t s of Main Ice Areas, Season of 194-9 0 19 L i m i t s of Main Ice Areas, Season of 1950 " 20 L i m i t s of Main Ice Areas, Season c f I95I M 21 L i m i t s of Main lee Areas, Season of 1952 • v i LIST OF PHOTOGRAPHS PHOTOGRAPH " PAGE 1 and 2 S t r i n g s of brash i c e o f f the north coast of Gaspe P e n i n s u l a , March 20, 1952 11 3 Edge of brash i c e o f f the mouth of Miramichi Bay, March 20, 1952 11 If- and 5 Landfast i c e , shore l e a d s , and open pack i c e along the north coast of Prince Edward I s l a n d , March 20, 1952 12 6 and 7 Pack ice of v a r y i n g s i z e d f l o e s o f f Miramichi Bay, March 20, I952 12 & Sheets of i c e breaking up o f f the New Brunswick coast south of the Bale de Chaleur, March 20, 1952 13 9 A f i e l d of c lose pack i c e off the New Brunswick coast south of the Bale de Ghaleur, March 20, 1952 13 CHAPTER I INTRODUCTION THE PROBLEM The fundamental aim ef the present study i s to d i s c o v e r the d i s t r i b u t i o n of i c e i n the breakup season and to t r a c e i t s behaviour throughout the months of March, A p r i l , and May. With t h i s d i s t r i b u t i o n and behaviour e s t a b l i s h e d , i t i s proposed to determine the r e l a t i v e inf luences on the i c e of the p h y s i c a l f a c t o r s of the environment. F i n a l l y , i t i s i n tended that a p i c t u r e of average condit ions throughout the i c e season should be presented. Ice d i s t r i b u t i o n i n the Gulf of St . Lawrence Is of utmost importance to s h i p p i n g . A l l ships entering the Great Lakes-St . Lawrence system must pass through the g u l f . The whole system i s blocked to navigat ion f o r nearly f i v e months of the year due to i c e c o n d i t i o n s . The condit ions i n the r i v e r can be r e a d i l y evaluated by d i r e c t observation from the l a n d , but the Gulf of St. Lawrence presents a d i f f e r e n t s i t u a t i o n . The area of the g u l f Is approximately equal to the com b i n e d areas of the four maritime p r o v i n c e s . I t i s impossible , t h e r e f o r e , to a s c e r t a i n the i c e c o n d i t i o n s over such a l a r g e area from observations taken along shore. At the beginning of the i c e season the l a s t vessels remaining i n the g u l f are able to keep each other posted concerning the ice condit ions i n t h e i r r e s p e c t i v e v i c i n i t i e s . On the other hand, because no 2 ships are operating i n the g u l f d u r i n g the winter other o b s e r v a t i o n a l arrangements must be made i n order to determine when n a v i g a t i o n can s a f e l y begin d u r i n g the breakup season. U n t i l 1940 t h i s estimate of i c e condit ions d a r i n g the breakup depended c h i e f l y on the r e p o r t s of the government icebreakers operating i n the g u l f . The information obtained was so s c a t t e r e d and incomplete, because there were so few v e s s e l s , that i t proved inadequate f o r the purpose. Conse quently , with the aim of d e c l a r i n g the g u l f open to n a v i g a t i o n as e a r l y as i c e condit ions i n a given area would p e r m i t , an a e r i a l i c e survey was inaugurated i n 1940 by the Depart ment of Transport . The survey has continued every spring since that time. The r e p o r t s of t h i s survey provide a wealth of information which simply d i d not e x i s t p r e v i o u s l y . SOURCES OF INFORMATION The Gulf of S t . Lawrence P i l o t 1 i s probably the most a u t h o r i t a t i v e source of publ ished information on i c e c o n d i t i o n s i n the g u l f . The treatment Is very b r i e f , however, and does not d e a l s p e c i f i c a l l y with the breakup season. Another government p u b l i c a t i o n , A r c t i c Ice on Our Eastern C o a s t , 2 by A . G. Huntsman, contains a short s e c t i o n concerning the Gulf of St . Lawrence, but the evaluation of i c e condit ions i s u n - ^-Department of Mines and Resources, Gulf of St . Law rence P i l o t , T h i r d E d i t i o n . Ottawa, 1946. ^Huntsman, "A. G . , A r c t i c Ice on Our Eastern Coast, B u l l e t i n No. 13, B i o l o g i c a l Board of Gltnada. Toronto, January, 1930. sound and abbreviated. The Ice A t l a s of the Northern Hemi sphere ,5 publ ished by the U . S. Navy, includes maps of the average l i m i t s of i c e f o r each month of the year i n the g u l f a r e a , however, these are highly g e n e r a l i z e d . O c c a s i o n a l l y , r e p o r t s of i c e conditions i n the g u l f appear i n the annual p u b l i c a t i o n of the I n t e r n a t i o n a l Ice Observation and lee P a t r o l Service i n the North A t l a n t i c Ocean,^ although no i n t e r p r e t a t i o n i s attempted. Mr. J . G . G . Kerry has w r i t t e n a number of a r t i c l e s d e a l i n g with ice i n the g u l f and the S t . Lawrence R i v e r (see b i b l i o g r a p h y , page 95). Again, h i s e s t i mate i s incomplete, e s p e c i a l l y In regard to the breakup sea son. These few works c o n s t i t u t e the main sources of pub l i s h e d information i n respect to i c e c o n d i t i o n s . E x t r a c t i o n of i c e information from a l l these sources and from a d d i t i o n a l unpublished and publ ished m a t e r i a l was c a r r i e d out by the author during the months from May to November, 1951, i n connection with the Canadian Ice D i s t r i b u t i o n Survey. This survey i s a p r o j e c t of the Geographical Branch, Department of Mines and T e c h n i c a l Surveys, Ottawa, and the author was engaged i n t h i s work of e x t r a c t i o n while i n the employ of the Branch. The main sources, besides the a e r - S. Navy, Hydrographie O f f i c e , lee A t l a s of the Northern Hemisphere, F i r s t E d i t i o n . Washington, 19457 k U. S. Treasury Department, Coast Guard, I n t e r n a t i o n a l l e e Observation and Ice P a t r o l Service i n the North A t l a n t i c Olean. WashlngtonT^WT-1949. 4 l a l i c e survey r e p o r t s , 5 from which extracts were taken were the reports of the I n t e r n a t i o n a l Ice P a t r o l S e r v i c e , ^ and the f i l e s of the Canadian Hydrographic S e r v i c e . 7 A l l the extracts were c l a s s i f i e d according to a r e g i o n a l d i v i s i o n of the g u l f . U n t i l recently the l a c k of data s u f f i c i e n t l y d e t a i l e d to support conclusions has prevented the furtherance of i n v e s t i g a t i o n i n t h i s f i e l d , but the appearance of the a e r i a l i c e survey r e p o r t s provides an almost unprecedented oppor t u n i t y f o r a d e t a i l e d study of ice condit ions i n the breakup season. The present study i s based p r i m a r i l y on these d a t a . U n f o r t u n a t e l y , the f l i g h t routes were confined to that part of the g u l f south of a l i n e from Heath P o i n t , A n t i c o s t i to the Bay of I s l a n d s , Newfoundland. As a r e s u l t , the Ice c o n d i t i o n s i n the northern p o r t i o n of the g u l f , i n c l u d i n g the S t r a i t of B e l l e I s l e , are not considered i n d e t a i l . S i m i l a r l y , i c e c o n d i t i o n s i n harbours and small e s t u a r i e s are not t r e a t e d i n d e t a i l because the i c e reports r e f e r c h i e f l y to the open areas of the g u l f . The normal procedure of the a e r i a l observers was t o make several f l i g h t s during March to a s c e r t a i n the quantity ^Department of Transport, "Reports of A e r i a l Ice Surveys i n the Gulf of S t . Lawrence, 1 1 P i l e No. 6262-3, g V o l s . Ottawa, 1 9 4 0 - 1 9 5 2 . c °U. S. Treasury Department, op. c i t . 7Department of Mines and Resources, Hydrographic S e r v i c e , "General Correspondence on Ice C o n d i t i o n s , 0 P i l e No. 6 3 4 , V o l . 3. Ottawa, I 9 2 2 - I 9 5 I . Department of Mines and Resources, Hydrographic S e r v i c e , "Questionnaire, Re: lee Conditions i n the Gulf of St . Lawrence," F i l e No. 6 3 4 , V o l . 1 . Ottawa, 1 9 3 7 . 5 and extent of i c e i n the g u l f before beginning d a i l y f l i g h t s , weather p e r m i t t i n g , toward the end of the month. These d a i l y f l i g h t s were general ly continued as long as i c e remained i n the g u l f , even i f t h i s n e c e s s i t a t e d making several f l i g h t s i n May. The routes followed were often v a r i e d from day to day i n order to give a complete coverage every few days of the s e c t i o n of the g u l f w i t h i n the bounds of the survey. The r e p o r t s were summarized and broadcast over the Maritime r a d i o s t a t i o n s f o r the immediate warning of vessels i n the a r e a . To i n d i c a t e the type of information contained i n these reports an excerpt from the Canadian lee D i s t r i b u t i o n Survey f i l e i s presented below. These data r e f e r to region 10 GD, Magdalen- S t . George, In the f i l e . A p r i l 4, 1942. "Prom 42.30 N . , 62.00 W., over steamer t r a c k to Gape Bay open water, from 23 miles southwest of Gape Ray i c e extends s o u t h eastward and to the Cape Breton Coast." A p r i l 9, 1942. "Large f i e l d s i g h t e d , southern l i m i t s 46.30 N . , 61.00 W. A p r i l 23, 1942. "No Ice between St . Paul I s l a n d and B i r d Rocks." A p r i l 24, 1942. "On a l i n e from Cape S t . George, Newfoundland, to Heath Point two small growlers 48.40 N . , 59.40 W., 46.40 N . , 60.00 W. West coast of Newfoundland c l e a r to v i c i n i t y of Bay of I s l a n d s , s t r i n g s and patches f o r t y miles off Heath Point n o r t h and south of t h i s l i n e , then l a r g e f i e l d s ten miles o f f Heath Point extending to Table Head, then southwestward to 46.20 N . , 62.40 W., to 46.30 N . , 63.30 W., to 46.55 N . , 63.15 W., to South P o i n t . " 8 Department of Mines and T e c h n i c a l Surveys, Geographical Branch, "Canadian Ice D i s t r i b u t i o n Survey P i l e , " Ottawa, 1951. 6 PROCEDURES Such d e t a i l e d information provided the b a s i s f o r a s e r i e s of maps d e p i c t i n g the i c e c o n d i t i o n s at ten-day i n t e r v a l s . An i n t e r v a l of t h i s length was necessary because of the blanks i n the record which occurred as a r e s u l t of adverse f l y i n g condit ions or incomplete coverage of the a r e a . The dates chosen were March 15, March 25, A p r i l 5, A p r i l . 1 5 , A p r i l 25, May 1, and May 5. The mapping at f i v e - d a y i n t e r v a l s a f t e r A p r i l 25 was made p o s s i b l e by the more accurate r e p o r t s l a t e r i n the season. Greater accuracy at t h i s time might be expected because the ice areas are so reduced that i t i s easy to carry out complete observations. The maps were designed to show the type of i c e - c o v e r at these dates with the use of s u i t a b l e symbols. Considerable i n t e r p o l a t i o n was necessary i n the c o n s t r u c t i o n of these maps, i n order that a complete p i c t u r e of the probable i c e con d i t i o n s on each date might be achieved. In s p i t e - o f t h i s n e c e s s i t y , the maps are considered as reasonably accurate. Supplementary notes p o i n t i n g out the changes i n i c e c o n d i t i o n s which occurred between the dates were w r i t t e n to accompany the maps. The t o t a l number of maps produced was s ixty-two. Some years r e q u i r e d more maps than o t h e r s , depending on the amount of information a v a i l a b l e and the date of f i n a l c l e a r i n g of the g u l f . These maps were too numerous, however, to f a c i l i t a t e ready comparison of separate years with a view toward determining the patterns and rates of breakup. 7 A procedure was e s t a b l i s h e d to reduce the m a t e r i a l to more manageable proportions without l o s i n g valuable d e t a i l . Upon i n s p e c t i o n of the s e r i e s of maps f o r each year and exami n a t i o n of the supplementary notes, i c e condit ions were de s c r i b e d i n d e t a i l . 9 At the same time, a new map was drawn f o r each season i n c o r p o r a t i n g the main features of the b a s i c maps. T h i s map showed the l i m i t s of the main i c e areas at each date. While i t gave no i n d i c a t i o n of the percentage or type of i c e - cover, i t depicted more g r a p h i c a l l y the ehanges i n p o s i t i o n of the i c e f i e l d s as the season progressed. Copies of these maps may be found i n the Appendix. Ice condit ions during the breakup i n these t h i r t e e n seasons were r e l a t e d to the determining p h y s i c a l f a c t o r s of the environment. The c o r r e l a t i o n w i t h the meteorological f a c t o r s was effected through the use of s t a t i s t i c s publ ished by the Meteorological D i v i s i o n , Department of Transport . Mainly government p u b l i c a t i o n s were consulted i n the exami n a t i o n of the other f a c t o r s . The d e s c r i p t i o n of average winter condit ions was based c h i e f l y on the data extracted from the Canadian Hydrographic Service f i l e s 1 0 and from the reports of the I n t e r n a t i o n a l Ice ^These d e s c r i p t i o n s are i n c l u d e d i n the complete report on i c e d i s t r i b u t i o n i n the Gulf of St. Lawrence during the breakup season which was submitted to the Geographical Branch, Department of Mines and T e c h n i c a l Surveys, Ottawa, i n September, 1952. •^Department of Mines and Resources, op. c i t . P a t r o l S e r v i c e . 1 1 The f i l e s contain the r e p l i e s to a q u e s t i o n n a i r e which was sent to skippers of v e s s e l s , l i g h t - k e e p e r s , and other persons who might he expected to possess knowledge of i c e c o n d i t i o n s . The reports of the I n t e r n a t i o n a l Ice P a t r o l Service o c c a s i o n a l l y contain references to the Gulf of St . Lawrence. This information, together with that from other sources, was s i f t e d and cross-checked In order to achieve an • e v a l u a t i o n of winter i c e conditions which was reasonably accurate. The accuracy of the d e s c r i p t i o n of s p r i n g i c e c o n d i t i o n s was b e t t e r s t i l l because i t was based on the a e r i a l survey r e p o r t s as w e l l as on the Hydrographic Service f i l e s . TERMINOLOGY A number of terms appear throughout the study which r e q u i r e d e f i n i t i o n s . Several of these terms have a s p e c i a l meaning i n t h i s context which may not coincide w i t h t h e i r meaning elsewhere, while others are accepted terms f o r i c e types. Included i n the f i r s t group are the terms " g u l f , " "breakup," " ice season," " l i g h t ice c o n d i t i o n s , " and "heavy i c e c o n d i t i o n s . " While "gulf" i s an abbreviated form f o r "Gulf of St . Lawrence," i t generally does not apply to the whole g u l f i n t h i s study, but r a t h e r to that part south of a l i n e from Heath P o i n t , A n t i c o s t i to the Bay of I s l a n d s , Newfoundland, f o r which area d e t a i l e d i c e Information i s a v a i l a b l e . When i t a p p l i e s to the whole Gulf of St . Lawrence the context makes that apparent. The word "breakup" i s used 1 1 U . S. Treasury Department, op. c i t . i n the f o l l o w i n g study i n a wide sense. Not only the a c t u a l breaking up of ice sheets i s i m p l i e d , but also the c l e a r i n g of i c e from the g u l f . "Ice season" i s understood as the p e r i o d from November to May when i c e i s present i n the g u l f . The term " l i g h t i c e c o n d i t i o n s " i s r e l a t i v e , i n d i c a t i n g that the i c e i n the g u l f Is l e s s extensive than i n other areas and mostly under two feet t h i c k . Conversely, the term "heavy i c e c o n d i t i o n s " i n d i c a t e s that the i c e i s r e l a t i v e l y extensive and t h i c k e r than two f e e t . The l i s t of i c e terms which fol lows i s adapted with m o d i f i c a t i o n s from a U. S. Hydrographic Office p u b l i c a t i o n on i c e t e r m i n o l o g y . 1 2 Some of the i c e types are i l l u s t r a t e d by the photographs on pages n , 12, and 13. Brash i c e - Small ice fragments l e s s than s i x feet across; the wreckage of other forms of i c e . Close pack D r i f t ice Fast i c e or l a n d f a s t Tee F i e l d F l o e Pack composed of f l o e s mostly i n contact . I t i s general ly unnavigable to ordinary s h i p s . Loose, very open pack, where water predominates over i c e . The f l o e s are usual ly smaller than i n close or open pack w i t h much r o t t e n i c e , and vessels can u s u a l l y pass through i t without a l t e r i n g course or speed. Sea ice which remains fast i n the p o s i t i o n of growth, found along coasts where It Is attached to the shore, or over shoals where It may be h e l d i n p o s i t i o n by i s l a n d s or grounded Icebergs. The l a r g e s t of i c e areas, greater than f i v e miles a c r o s s . A piece of sea ice other than f a s t i c e , l a r g e or s m a l l . A*=U. S. Navy, Hydrographic O f f i c e , "A F u n c t i o n a l Glossary of Ice Terminology," Study No. 103, P r o v i s i o n a l , May, 1946. 10 Growler L i g h t Ice Open pack A small p i e c e of g l a c i e r Ice, usual ly greenish i n colour and barely showing above the water. Heavy Ice - Any t h i c k f l a t i c e . Lead - A passage through pack i c e . Leads may form e i t h e r by the widening of a crack or by a general loosening of the f l o e s . A shore- lead i s a s t r e t c h of navigable open water formed when pack i c e moves away from the f a s t i c e under the influence of wind or t i d e . - Ice of medium t h i c k n e s s , l e s s than two f e e t . - Pack composed of f l o e s which f o r the most part do not touch. B e l t s are usually narrow with many leads and p o o l s . E a s i l y navigable but speed i s slow and changes of course c o n t i n u a l l y necessary. Pack i c e - Sea ice which has d r i f t e d from i t s o r i g i n a l p o s i t i o n . Pool - Any enclosed sea-water i n the pack, other than a l e a d . Sheet ice - A l a r g e piece of f l o e ice that d r i f t s to sea unbroken. ORGANIZATION The p h y s i c a l geography of the Gulf of St . Lawrence, i n c l u d i n g the s u b a e r i a l and submarine morphology, the movements and p h y s i c a l c h a r a c t e r i s t i c s of the water, and the e l i m a t e , i s examined i n general d e t a i l . Average winter i c e c o n d i t i o n s are then discussed by months. With t h i s back ground, the a c t u a l observed ice d i s t r i b u t i o n during the break up seasons of ISkO to 1952, i n c l u s i v e , i s presented, together w i t h an i n d i c a t i o n of the a i r temperatures which p r e v a i l e d throughout the ice season. Maps of i c e l i m i t s at s p e c i f i e d dates i n A p r i l and temperature graphs accompany t h i s p r e s e n t a t i o n of data. Based on t h i s d a t a , the patterns and rates Photos. 1 and 2. Strings of brash ice o f f the north coast of Gaspe Peninsula, March 20, 1952 (courtesy of Miss I. M. Dunbar). • Photo. Edge of brash ice o f f the mouth of Miramichi Bay, March 20, 1952 (courtesy of Miss I. M. Dunbar). Photos. K and 5. Landfast i c e , shore l e a d s , and open pack Ice along the north coast of P r i n c e Edward I s l a n d , March 20, 1952 (courtesy of Miss I . M. Dunbar and Miss M. R. Montgomery). Photos. 6 and 7. Pack i c e of v a r y i n g s i z e d f l o e s off Miramiohi Bay, March 20, I952 (courtesy of Miss I . M. Dunbar and Miss M. R. Montgomery). Photo. g. Sheets of ice breaking up off the New Brunswick coast south of the Baie de Chaleur, March 20, 1952 (courtesy of Miss I . M. Dunbar). Photo. 9. A f i e l d of close pack i c e off the New Brunswick coast south of the Baie de Chaleur, March 20, I952 (courtesy of Miss I . M. Dunbar). of breakup are i s o l a t e d and c l a s s i f i e d . Then the p h y s i c a l f a c t o r s d i s c u s s e d at the beginning are re-examined with the aim of r e l a t i n g them to the d i s t r i b u t i o n and behaviour of the i c e and determining t h e i r i n f l u e n c e . F i n a l l y , the general conclusions are stated and the average i c e condit ions during March and A p r i l are d e s c r i b e d . T h i s d e s c r i p t i o n complements the statement of winter i c e c o n d i t i o n s , thereby g i v i n g the e n t i r e p i c t u r e of the i c e season. The map f o l l o w i n g page Ik- shows the l o c a t i o n s of places mentioned i n the t e x t . N E W F O U N D L A N D G U L F OF ST. LAWRENCE c % /SH I P P I G AN C A P E A N G U I L L E C A P E R A Y L M A G D A L E N S T P A U L I C A P E *1 0 R T H N E W PRINCE EDWARD ISLAND M l Q U E L O N \ . \ f ^ a o B R U N S W I C K V , — - ' L O U I S B U P G SCATA Rl I. MAP G U L F O F S T . L A W R E N C E PLACE NAMES SCALE IN MILES 20 40 Map 1 (to follow page 1H-) 5 1 4 9 < A T 4 5 < 62' 6 01 CHAPTER I I PHYSICAL GEOGRAPHY SUB AERIAL AND SUBMARINE MORPHOLOGY The Gulf of St . Lawrence l i e s on the boundary between two physiographic p r o v i n c e s . On the north the g u l f i s bounded by the Precambrian rocks of the Canadian S h i e l d and on the west, south, and east c h i e f l y by the Palaeozoic r o c k s , g r e a t l y f o l d e d and f a u l t e d , of the Appalachian Highlands Province. Two main ranges of the Appalachian system are traceable i n the r e g i o n . These are the Shickshock Range of Gaspe p e n i n s u l a and the highlands of Nova S c o t i a , which continue northeastward as the Long Range of Newfoundland. The f o l d mountains of Gaspe curve southeastward toward the Nova S c o t i a range before d i s appearing below the waters of the g u l f , while the southern range maintains i t s northeast-southwest t r e n d , thereby en c l o s i n g the g u l f . The g u l f I t s e l f i s much deeper north of a l i n e from Cape Gaspe to St . Paul Is land than south of i t ( see map f o l l o w i n g page 15). A submarine canyon, whose bottom depths range from 150 to JQQ fathoms below the surface, traverses the. g u l f from the estuary of the St . Lawrence R i v e r past Gaspe, north of the Magdalen Is lands, through Cabot S t r a i t and southeastward to the edge of the c o n t i n e n t a l s h e l f where !3Atwood, W. W., The Physiographic Provinces of North America. Boston: Ginn and Company, 1940, p . 67. ~ i t separates Bank St. P i e r r e from Banquereau Bank. Branches of t h i s canyon extend up the northeast arm of the g u l f toward the S t r a i t of B e l l e I s l e and northwestward between A n t i c o s t l I s l a n d and the Quebec mainland. These steep-walled canyons are 40 to 100 miles broad and occupy much of the northern and eastern sect ions of the g u l f . On the other hand, the f l o o r of the roughly c i r c u l a r area south of the transverse canyon l i e s l e s s than f i f t y fathoms below the s u r f a c e . 1 ^ Ice Is more l i k e l y to form i n shallow areas because there i s not so great a body of water which must be cooled before f r e e z i n g can take p l a c e . Of the three s t r a i t s connecting the g u l f with the open A t l a n t i c , Cabot S t r a i t i s the widest. I t i s apparent that a g r e a t e r volume of Ice w i l l gain e x i t from the g u l f through t h i s s t r a i t during the breakup season than through e i t h e r the S t r a i t of B e l l e I s l e or the S t r a i t of Ganso. Because the S t r a i t of Canso i s e s p e c i a l l y narrow, the southern part of the g u l f i s more confined than the c e n t r a l s e c t i o n and ice movement i s r e s t r i c t e d . S i m i l a r l y , the northeast arm i s c o n f i n e d , but the S t r a i t of B e l l e I s l e provides a wider l i n k with the open ocean. A n t l c o s t i I s l a n d , the Magdalen I s l a n d s , and Prince Edward I s l a n d tend to h i n d e r the free movement' of i c e over the surface of the g u l f . The shorel ines of the Gulf of St. Lawrence area are c l a s s i f i e d as primary or y o u t h f u l , t h e i r c o n f i g u r a t i o n being ^ S m i t h , F . G . G . "Hydrographical F e a t u r e s , " Canada Year Book 194?. Ottawa, 1 9 4 7 , p . 7 . due mainly to non-marine erosive f o r c e s . ! 5 These coasts are formed c h i e f l y hy the drowning of f o l d e d , f a u l t e d , and g l a c i ated topography and, as a r e s u l t , they are d i v e r s e i n form. The shorel ines are c h a r a c t e r i z e d throughout by indentations which conform e s s e n t i a l l y with the alignment and the nature of the rock s t r u c t u r e . 1 0 I t i s notable that the western and southern s h o r e l i n e s of the g u l f have numerous broad, shallow embayments i n contrast to the Precambrian s h o r e l i n e , bounding the g u l f on the n o r t h , where the bays are small and the water Is deep o f f s h o r e . The broad, shallow bays provide great areas of p r o t e c t e d water surface where i c e forms more r e a d i l y and where the breakup i s slower than i n unprotected r e g i o n s . The detainment of the i c e during the breakup season i s p a r t i c u l a r l y n o t i c e a b l e i n the Baie de Chaleur because the mouth of the bay i s narrowed by Miscou and Shippigan i s l a n d s . On the other hand, the smooth n o r t h coast of Gaspe does not hinder the free d r i f t of i c e i n t o the g u l f during the breakup. WATER MOVEMENTS AND PROPERTIES Within the physiographic framework of the g u l f the water movements and p r o p e r t i e s g r e a t l y affect the behaviour of f l o a t i n g i c e . Among the f a c t o r s which cause movement are the t i d e s , t i d a l c u r r e n t s , and ocean c u r r e n t s . 1 5shepard, F r a n c i s P . , Submarine Geology. New York: Harper and B r o t h e r s , 1946, p. JW. •^Johnson, Douglas W., The New England-Acadian S h o r e l i n e . New York: John Wiley and Sons, 1925, p. 20-23. Tides and T i d a l Currents Tides are wave motions which involve no appreciable h o r i z o n t a l movement of water, but r a t h e r , a v e r t i c a l r a i s i n g and lowering of the water i n r e l a t i o n to a datum p l a n e . They are generated p r i n c i p a l l y i n the open oceans of the world and not i n the confined c o a s t a l basins where they are most n o t i c e a b l e . 1 ? The t i d a l undulation enters the g u l f mainly through Cabot S t r a i t and progresses i n a counter-clockwise d i r e c t i o n around a c e n t r a l point west of the Magdalen I s l a n d s . 1 ^ The disturbance of the water surface by t i d e h i n ders the formation of l a r g e sheets of i c e and a i d s i n the breaking up of sheets which have become e s t a b l i s h e d . This s h a t t e r i n g a c t i o n i s more e f f e c t i v e where the t i d a l ranges are h i g h . The range of t i d e i n the open ocean i s seldom more than 1 metre, but t h i s i s a m p l i f i e d along shallow c o a s t l i n e s , i n many cases, by t i d a l components other than those which are g r a v i t a t i o n a l i n n a t u r e . 1 9 On the map of t i d a l ranges i n the g u l f , f o l l o w i n g page 19, the l i n e s j o i n places having equal ranges of s p r i n g t i d e s . w These v a l u e s , expressed i n metres, 1 7 S t e w a r t , John Q . , Coasts, Waves and Weather. Boston: Ginn and Company, 1945, P. 207. Kriegsmarlne, Ubootshandbuch der Ostkdste Kanadas ( A t l a s ) . B e r l i n , 1942, p . l b b . ^ S t e w a r t , op. c i t . , p. 192. 2 0 When the g r a v i t a t i o n a l p u l l s of the sun and moon are combined along the same l i n e , as occurs at new and f u l l moon, the t i d e s produced are both h i g h e r and lower than at other t imes. These are termed s p r i n g t i d e s . are computed from t i d e t a b l e s which do not include the extremes caused by meteorological c o n d i t i o n s . Because the readings employed were taken at c o a s t a l s t a t i o n s , adjustments were nec e s s a r i l y made i n order that average values f o r the offshore areas might be d e r i v e d . As a r e s u l t , f i g u r e s f o r some c o a s t a l s t a t i o n s may not appear to f i t the p a t t e r n i n d i c a t e d . Ranges i n the g u l f are not g r e a t , as a r u l e , but are h i g h e r toward the estuary of t h e - S t . Lawrence R i v e r and i n Northumberland S t r a i t than elsewhere. In these areas t i d a l s h a t t e r i n g i s most pronounced. Prom the mouth of the estuary where the range i s 1.5 metres the range increases upstream to more than 3 metres above Pointe des Monts. In the v i c i n i t y of Gape Tormentlne i n Northumberland S t r a i t the range i s 1.5 metres. Ranges l e s s than 0.5 metres are c h a r a c t e r i s t i c of the area west of the Magdalen I s l a n d s , consequently, the effect of t i d e s on i c e sheets i n t h i s area i s minimized. When t i d a l undulations progress through shallow water an a c t u a l h o r i z o n t a l movement of the water takes p l a c e . Such h o r i z o n t a l movements are termed t i d a l c u r r e n t s . These c u r r e n t s seldom coincide with the time of h i g h water, although they are reversed i n rhythm with the t i d e s . T h e i r v e l o c i t i e s are g e n e r a l l y l e s s than 1 knot i n open a r e a s , but i n the S t r a i t of Ganso the t i d a l currents are, decidedly stronger. In Northumberland S t r a i t the currents flow from both entrances meeting i n the middle o f f Bale Verte and t h e i r strengths are approximately 1 to 1.5 knots. The S t r a i t of B e l l e I s l e has c u r r e n t s which are t i d a l In c h a r a c t e r , but i n a d d i t i o n , there i s a dominant flow i n one d i r e c t i o n o r the other f o r periods 70° 66" 62° 58° 54° of a week or m o r e . d l The v e l o c i t i e s i n the s t r a i t range between 0.5 and over 2 knots. In most other s e c t i o n s of the g u l f the t i d a l currents are weak and i l l - d e f i n e d . Winds are e f f e c t i v e In checking or i n c r e a s i n g the v e l o c i t y of t i d a l c u r r e n t s . Ocean Currents Superimposed upon the system of t i d e s and t i d a l currents i s a system of constant ocean c u r r e n t s . In t h i s respect the Gulf of S t . Lawrence i s c h a r a c t e r i z e d by a c o u n t e r clockwise c i r c u l a t i o n (see map f o l l o w i n g page 21). Water from the ocean pours i n t o the g u l f around Gape Ray and, due to the inf luence of the e a r t h ' s r o t a t i o n , i t curves to the r i g h t and flows northeastward along the west coast of Newfoundland as f a r as Point Riche. At Gape Ray the c u r r e n t , a b e l t near shore ten to f i f t e e n miles i n width, has a v e l o c i t y of a l i t t l e l e s s than 1 knot. Prom Gape St. George to the Bay of Islands the movement of the water i s hardly a p p r e c i a b l e , but northward of t h i s p o i n t i t i s constant at about 1 knot, stronger near land than o f f s h o r e . 2 2 The current has the b e n e f i c i a l effect of keeping the southwest and west coasts of Newfoundland free of ice l a t e r than other areas w i t h i n the g u l f . Much of the water i n t h i s current departs from the stream and spreads out northwestward, heading across 2 1A1 t h o u g h the cause of t h i s dominant flow i s not f u l l y known, i t i s thought to be c h i e f l y m e t e o r o l o g i c a l . 2 2 Department of Mines and Resources, Gulf of St. Lawrence P i l o t , T h i r d E d i t i o n . Ottawa, 1946, p . LVI. the g u l f i n a weak movement to A n t i c o s t l I s l a n d . In f a c t , the preponderance of flow i n t h i s whole northern area to a c o n s i d erable depth i s toward the St . Lawrence estuary, although the v e l o c i t i e s are low and the d i r e c t i o n of movement i s r e a d i l y a f f e c t e d by the wind. Nevertheless, a great quantity of ice i s c a r r i e d southward and westward from the S t r a i t of B e l l e I s l e a r e a . The currents i n the s t r a i t i t s e l f are e n t i r e l y t i d a l i n c h a r a c t e r . At the mouth of the St. Lawrence River water from the northern part of the g u l f combines with that from the r i v e r to generate the Gaspe Current. The current begins at Gap Chat and, d e f l e c t e d to the r i g h t , i t hugs the Gaspe coast as i t flows eastward. Although It i s constant at an average v e l o c i ty of 2 k n o t s , the t i d e s do cause v a r i a t i o n s i n speed, i n s p i t e of the fact that they cannot reverse or completely check the flow. The approximate width of the current i s twelve m i l e s and i t seldom extends f u r t h e r than fourteen miles offshore. 23 A l a r g e amount of i c e formed i n the St . Lawrence r i v e r and estuary i s deposited i n the g u l f by the Gaspe Current. Leaving Gape Gaspe the current flows southeastward, but the v e l o c i t y i s much reduced and i t spreads over a wide a r e a , f i l l i n g up the c e n t r a l part of the g u l f . The predomi nant d r i f t i n t h i s c e n t r a l s e c t i o n Is eastward across to the Magdalen Islands and Cape Breton. The v e l o c i t y , however, i s only 0 .5 to 1 knot and there Is no constant current 2 5 l b l d . , p. LIX. 22 d i s c e r n i b l e . 2 ^ " In the southern part of the g u l f , p a r t i c u l a r l y In Northumberland S t r a i t , the currents are t i d a l i n character. The l a c k of constant currents i n t h i s s e c t i o n of the g u l f permits the accumulation and stagnation of ice i n t h i s area on some occasions. The Gaspe Current i s rejuvenated i n i t s c o n t i n u a t i o n by the c o n s t r i c t i o n of Cabot S t r a i t . An 18-mile-wide current comparable i n constancy with the Gaspe Current flows along the Cape Breton coast a few miles off Cape North. Fed c h i e f l y by a dominant flow of water southeastward from the northern end of the Magdalen Is lands to Gape North, i t s v e l o c i t y at times reaches 2 k n o t s . 2 5 The Cape Breton current extends as a weak flow along the coast, often as f a r as S c a t a r l I s l a n d . This current i s of great Importance In t r a n s p o r t i n g i c e from the g u l f , e s p e c i a l l y during the breakup. Most of the r i v e r s which flow i n t o the g u l f , except the S t . Lawrence/ are too small to give r i s e to s i g n i f i c a n t c u r r e n t s . In a d d i t i o n , t h e i r effect on the c l e a r i n g of Ice from the g u l f i s minor beeause the bulk of the Ice In the g u l f discharges through Cabot S t r a i t before the r i v e r s break up. P h y s i c a l P r o p e r t i e s As p a r t of the A t l a n t i c Oeean, the Gulf of St . Lawrence Is f i l l e d w i t h s a l t water s l i g h t l y modified i n ^^Department of the Naval S e r v i c e , The Currents In the Gulf of St. Lawrence. Ottawa, 1913, p. 11. ^Department of Mines and Resources, op. c i t . , p. L V I . c e r t a i n sect ions by the a d d i t i o n of f r e s h water. I n v e s t i gations have determined that i n the southwestern h a l f of the g u l f , south of a l i n e from G-aspe to St. Paul I s l a n d , the water i s warmer and of lower density than i n the northeastern h a l f . The density i n . t h i s northeastern s e c t i o n i s much the same as i n the open A t l a n t i c . The G-aspe and Gape Breton currents are comparable i n having decidedly lower d e n s i t i e s than the waters outside the c u r r e n t s . 2 ^ The temperature c h a r a c t e r i s t i c s are not w e l l known, but i t i s e s t a b l i s h e d that a c o l d l a y e r of water l y i n g at a depth of about 50 fathoms i s constantly at a temperature near the f r e e z i n g point and that i t separates warmer l a y e r s both above and below. The water above 3 Q fathoms i s i n f l u e n c e d by the temperature of the a i r i n contact with i t . 2 7 Regarding surface temperatures, whieh have the greatest bearing on the . i c e formation process, I t i s d e f i n i t e that i n most sections of the g u l f the surface water temperatures do f a l l below the f r e e z i n g p o i n t of s a l t water. Ice formation Is e s p e c i a l l y pronounced around the Magdalen Islands and i n the shallow bays and s t r a i t s , i n c l u d i n g the Bale de Chaleur and North umberland S t r a i t . Throughout the open g u l f , however, i c e i s ^Department of the Naval S e r v i c e , op. c i t . , p. 36. 2?Department of the Naval S e r v i c e , Temperatures and D e n s i t i e s of the Waters of Eastern Canada. Ottawa, 1922, P- 7. not formed on a large scale due to a g i t a t i o n of the water and the greater d e p t h s . 2 ^ CLIMATE The climate of the Gulf of St . Lawrence region i s not so marine i n character as might be expected, c o n s i d e r i n g i t s l o c a t i o n . Lying i n the b e l t of Westerly Winds, the area i s mainly under the influence of a i r which moves from l a n d to sea. The path of the most frequent c y c l o n i c storms passes d i r e c t l y across the c e n t r a l part of the g u l f . This c o n t i n e n t a l a i r i s modified to a c e r t a i n extent, r e s u l t i n g i n more moderate c o n d i t i o n s than those which are experienced i n l a n d . Because the meteorological records are taken on l a n d i t i s .- necessary to g e n e r a l i z e concerning the condit ions over the g u l f . The temperature w i l l be more moderate over the water and the p r e c i p i t a t i o n lower, as a r u l e . Winds may achieve g r e a t e r v e l o c i t y i n view of the fact that obstruct ions are l a c k i n g . S a l t water does not behave i n the same manner as f r e s h water when i t i s cooled. The maximum density of f r e s h water i s at k-°0. When a body of water has been cooled to t h i s temperature, from top to bottom, f u r t h e r c o o l i n g at the surface w i l l not perpetuate the convection c u r r e n t s , but w i l l l e a d to more r a p i d c o o l i n g and eventual i c e formation at 0 G G . S a l t water reaches i t s c o n d i t i o n of greatest density at -2°C, which i s s l i g h t l y below i t s f r e e z i n g p o i n t ( - l . g ° C ) . As a r e s u l t , convection currents are generated that keep r e p l a c i n g the surface water u n t i l , and i f c o n d i t i o n s permit, even a f t e r i t reaches i t s f r e e z i n g p o i n t . The f r e e z i n g of s a l t water i s thus retarded -by i t s p h y s i c a l p r o p e r t i e s . In a d d i t i o n , the disturbance and mixing of the water by winds, t i d e s , and c u r r e n t s p l a y s an important r o l e i n the i c e formation process. 25 Temperature During the winter the isotherms tend to run northeast- southwest across the g u l f (see map f o l l o w i n g page 25). The Cabot S t r a i t region experiences temperatures about ten degrees Fahrenheit higher than those of the Quebec north shore because of the moderating influence of the open A t l a n t i c . This d i f f e r e n c e i n temperature i s r e f l e c t e d i n the dates of c l o s i n g of n a v i g a t i o n i n harbours throughout the gulf (see map f o l l o w i n g page 32). The harbours i n the southeastern p a r t of the g u l f freeze l a t e r than those i n the northwestern p a r t . The accompanying t a b l e , page 26, Indicates that average monthly temperatures throughout the g u l f drop below the f r e e z i n g point i n December and remain there u n t i l A p r i l . I t i s apparent that the a i r temperature i s low enough to give r i s e to i c e formation even on s a l t water I f other f a c t o r s combine to make i t p o s s i b l e . In the event that i c e does not form, temperature c o n d i t i o n s are such as to preserve ice which may have formed elsewhere and d r i f t e d i n t o the g u l f . Temper atures are s t i l l near f r e e z i n g during A p r i l when the breakup i s w e l l advanced. The v a r i a b i l i t y of i c e season temperatures i s h i g h . In a given year the d i f f e r e n c e from average of the mean monthly temperature might be f i v e or ten degrees at many s t a t i o n s i n the g u l f a r e a . Frequently , several consecutive months i n one season experience temperatures somewhat higher or lower than average. The severi ty of ice condit ions i s l a r g e l y dependent on these year to year f l u c t u a t i o n s of ISOTHERMS OF MEAN MONTHLYc T E M P E R A T U R E D E C R E E S F A H R E N H E I T C C L I M A T I C S U M M A R I E S , 1 9 4 8 ) M A P S Map 5 (to f o l l o w page 25). TABLE I MONTHLY AVERAGES OF DAILY MEAN TEMPERATURE M e t e o r o l o g i c a l S t a t i o n * November December January February March A p r i l Beraimis 27 14 2 8 20 33 Father P o i n t 29 17 9 11 22 34 Clarke C i t y 26 11 2 6 18 31 Natashquan 22 13 6 6 17 30 H a r r i n g t o n Harbour 28 13 8 9 20 30 Cap Chat 32 19 13 13 22 33 Cap Magdalen 31 18 11 14 21 32 E l l i s Bay 30 18 13 12 20 31 A n t i c o s t i (S.W.Pt.) 30 20 12 12 21 31 Gaspe" 30 17 10 11 22 33 P o r t D a n i e l 31 19 12 12 27 34 Bathurst 32 18 10 11 24 36 Chatham 33 19 12 12 23 37 Rezton 36 30 13 14 23 33 Summers!de 36 24 18 18 26 37 Charlottetown 23 18 17 26 36 A l l i s t o n 38 26 20 20 28 37 A n t i g o n i s h 38 27 20 18 28 37 Chetieamp 52 29 22 20 27 36 Baddeck 38 27 27 20 26 37 Sydney 38 29 29 20 27 36 Grindstone Island 36 23 19 16 23 32 S t . Paul Island 37 27 27 18 2 £ 32 Burgeo 33 29 23 21 26 33 Channel 36 28 22 21 23 33 S t . Georges 33 28 21 16 24 33 Corner Brook 34 23 18 18 23 33 i F o r l o c a t i o n s o f m e t e o r o l o g i c a l s t a t i o n s see map f o l l o w i n g page 40. 27 temperature. Consequently, In the examination of i c e con d i t i o n s during a t h i r t e e n - y e a r p e r i o d , i t i s d e s i r a b l e to r e l a t e the r e s u l t s to the observed temperatures of each year as w e l l as to the average temperatures. P r e c i p i t a t i o n Abundant p r e c i p i t a t i o n which i s evenly d i s t r i b u t e d throughout the year i s c h a r a c t e r i s t i c of the G-ulf of St . Lawrence area. Most s t a t i o n s receive more than ko inches a y e a r . There i s a s l i g h t summer maximum i n the more c o n t i n e n t a l northwestern part of the g u l f and a winter maximum i n the more maritime southeastern p a r t . Snowfall i s f a i r l y h i g h i n the g u l f a r e a , ranging from 60 to over 200 inches. The higher t o t a l s are recorded along the north shore and the lower t o t a l s i n the southeastern s e c t i o n . The effect of p r e c i p i t a t i o n on i c e formation and breakup i n the g u l f i s minor compared to that of temperature o r wind. Wind The wind roses (see maps f o l l o w i n g page 27) i l l u s t r a t e the percentage frequencies of wind by d i r e c t i o n f o r January and A p r i l , which months represent the p e r i o d when i c e i s found i n the Gulf of St . Lawrence. Winds of a westerly component p r e v a i l throughout most of the year, although i n spring and summer t h e i r prominence i s l e s s n o t i c e a b l e . At t h i s l a t t e r time of year the winds are more v a r i a b l e i n d i r e c t i o n and e a s t e r l y winds occur more frequently than at other seasons. Changes i n d i r e c t i o n , even complete r e v e r s a l s , may be expected PERCENTAGE FREQUENCY OF WIND P E R C E N T A G E O F W I N D 4 0 i 2 4 I ? ? ( C L I M A T I C S U M M A R I E S , 1 9 4 8 ) N U M B E R S I N D I C A T E T H E P E R C E N T A G E O F C A L M S MAP e Map 6 (to f o l l o w page 27) w i t h i n very short periods of time due to the c i r c u l a t i o n of the m i d - l a t i t u d e depressions which move across the area i n an almost constant procession i n winter. I t i s t h i s f e a t u r e , t y p i c a l of the b e l t of Westerly Winds, which i s r e s p o n s i b l e f o r the h i g h l y v a r i a b l e weather c o n d i t i o n s of the g u l f r e g i o n . The wind i s e f f e c t i v e i n c o n t i n u a l l y s h i f t i n g the pack i c e which covers most of the g u l f i n winter. Due to the r o t a t i o n of the e a r t h , the d r i f t of f l o a t i n g pack i c e i n the northern hemisphere i s about t h i r t y degrees to the r i g h t of the wind d i r e c t i o n . In general terms, however, the p r e v a i l i n g westerly winds carry the ice eastward toward Gabot S t r a i t , while n o r t h e r l y winds tend to pack the i c e i n the southern part of the g u l f . Southerly winds u s u a l l y accelerate the c l e a r i n g of i c e , but e a s t e r l y winds h o l d the i c e i n the g u l f . The sudden changes of wind d i r e c t i o n which are t y p i c a l of the r e g i o n cause l o c a l changes i n the p o s i t i o n of pack i c e , such as the opening or c l o s i n g of leads and p o o l s . SUMMARY Tides disengage landfast i c e and break up sheets of i c e formed i n shallow water. Much of t h i s ice i s c a r r i e d i n t o the open g u l f by t i d a l and ocean c u r r e n t s , adding to the supply of i c e which i s l a r g e l y r e t a i n e d i n the g u l f by the confined nature of the b a s i n . The a i r temperatures are low enough to preserve t h i s i c e and to encourage l o c a l ice f o r mation throughout the season. During t h i s time the f a c t o r s . . . . 2 q c a u s i n g i c e movement, p r i n c i p a l l y winds and c u r r e n t s , keep much of the i c e s h i f t i n g and c a r r y some of i t to the open ocean through Cabot S t r a i t . CHAPTER I I I WINTER ICE CONDITIONS Ice condit ions i n the Gulf of St . Lawrence during the months from November to March are not w e l l known. No r e g u l a r a e r i a l survey has been c a r r i e d out and few records taken aboard ship have been preserved. Much of the information which i s a v a i l a b l e , f o r example, r e p o r t s of s k i p p e r s , l i g h t - keepers, and other shore observers, r e f e r s to very l i m i t e d areas and may not be h i g h l y r e l i a b l e . The f o l l o w i n g d i s cussion c o n s t i t u t e s an attempt to present the general p i c t u r e as i n d i c a t e d by observations which can be substantiated. Although condit ions vary great ly from year to year, only average condit ions are i m p l i e d . The i s l a n d of Newfoundland acts as a b a r r i e r sepa r a t i n g the Gulf of St . Lawrence i c e from the A r c t i c i c e . The S t r a i t of B e l l e I s l e admits a quantity of i c e which i s s u f f i c i e n t to f i l l the northeast arm. Most of t h i s i s pack i c e which o r i g i n a t e d as l a n d f a s t i c e along the coast of Labrador. Icebergs seldom gain entrance to the g u l f ; they d r i f t southward i n the main stream of the Labrador Current. Consequently, pack ice c o n s t i t u t e s the bulk of the Gulf of S t . Lawrence i c e . Winter navigation In the g u l f i s r e s t r i c t e d . The Clarke Steamship Company operates a winter service with i c e - breaking vessels from Tadoussac to Seven Islands and some times as f a r east as Havre St. P i e r r e . This i s made p o s s i b l e by the f a c t t h a t frequent northwest winds push the i c e o f f shore. In Northumberland S t r a i t an i c e - b r e a k i n g f e r r y con n e c t s P r i n c e Edward I s l a n d w i t h the mainland, and a f e r r y operates between Cape Breton I s l a n d and Newfoundland. In a d d i t i o n to these r e g u l a r s e r v i c e s , n a v i g a t i o n i s c a r r i e d on by Canadian Government i c e - b r e a k e r s and by s m a l l s e a l i n g v e s s e l s . The i c e - b r e a k e r s , two or t h r e e i n number, a s s i s t those s h i p s attempting n a v i g a t i o n and c r o s s the g u l f o c c a s i o n a l l y while en route from the Cape Breton area to the S t . Lawrence R i v e r . On the whole, commercial n a v i g a t i o n ceases i n most s e c t i o n s of the g u l f about the middle of December, or e a r l i e r . The map f o l l o w i n g page 32 i n d i c a t e s the average date of the c l o s i n g of n a v i g a t i o n at v a r i o u s harbours i n the g u l f . In keeping w i t h the c h a r a c t e r i s t i c s of c l i m a t e , i t i s apparent t h a t the harbours nearest the open A t l a n t i c f r e e z e l a t e r than those which are more removed from the marine i n f l u e n c e . DECEMBER When the surface water temperatures i n the northern p a r t of the g u l f drop below f r e e z i n g p o i n t d a r i n g l a t e November, i c e begins t o form i n the n o r t h e a s t arm, e s p e c i a l l y i n the shallow bays and c o n f i n e d s t r e t c h e s of water. T h i s i c e i s very l i g h t and no a p p r e c i a b l e amount forms u n t i l December. In a d d i t i o n to i c e produced by l o c a l f r e e z i n g , heavy pack i c e begins to enter the g u l f through the S t r a i t of B e l l e I s l e l a t e In December. In s p i t e of the f a c t t h a t i c e c o n d i t i o n s are not serious i n the S t r a i t of B e l l e I s l e through out most of t h i s month, navigation general ly ceases about December 1. Ice forms f a i r l y early i n the lower St . Lawrence R i v e r and estuary and along the north shore of the g u l f because these areas are removed from the moderating influence of the open A t l a n t i c . Large sheets of i c e seldom develop u n t i l January, however. Such f a c t o r s as wind, t i d e , and current churn the water, breaking up the young i c e sheets before they have grown to a thickness which w i l l r e s i s t these a t t a c k s . A l a r g e quantity of ice broken by t i d a l a c t i o n In the St. Lawrence estuary i s c a r r i e d i n t o the g u l f by the G-aspe Current. This process begins i n l a t e December a f t e r the upper reaches of the r i v e r have already c o n t r i b u t e d ice to the g u l f . Corresponding c l o s e l y with the advent of low a i r temperatures throughout the g u l f , the f r e e z i n g of harbours occurs l a t e r i n the southern and southeastern areas. Even here n a v i g a t i o n i s not customary a f t e r the end of the f i r s t week In December. Although the Bale de Ghaleur does not freeze u n t i l the l a t t e r h a l f of the month, due to the great s i z e of the body of water, the smaller bays and harbours along the western side of the g u l f freeze before December 15. Ice o r i g i n a t i n g i n the St. Lawrence R i v e r i s c a r r i e d i n t o the g u l f by the Gaspe Current and by westerly winds and spreads out i n southern areas where constant currents are l a c k i n g , f i l l i n g Northumberland S t r a i t by the beginning of January. The route through the S t r a i t of Ganso i s c l o s e d to n a v i g a t i o n about January 1, due to the b l o c k i n g of the n o r t h e r n entrance by i c e , although the s e c t i o n south of Mulgrave r e mains open. Many of the harbours s i t u a t e d a l o n g the Nova S c o t i a and P r i n c e Edward I s l a n d c o a s t s do not f r e e z e u n t i l l a t e December, or i n some cases, u n t i l l a t e January. Cabot S t r a i t remains c l e a r throughout December. JANUARY By January the water temperatures have been lowered s u f f i c i e n t l y t o give r i s e to a l a r g e - s c a l e p r o d u c t i o n of i c e . Pack i c e formed i n the g u l f u s u a l l y ; a t t a i n s a t h i c k n e s s of two to f o u r f e e t . Because of lower temperatures and a l o n g e r i c e season, Labrador pack i c e i s t h i c k e r , sometimes up to seven f e e t . The growlers which e n t e r the g u l f may be con s i d e r a b l y t h i c k e r . O c c a s i o n a l l y , a sheet of i c e i s b u c k l e d Into r i d g e s as a r e s u l t of pressure caused mainly by powerful winds. S e v e r a l t h i c k n e s s e s of i c e may be p i l e d one above the o t h e r forming a mass as t h i c k as twelve or f i f t e e n f e e t . Such r i d g e s occur most f r e q u e n t l y i n the v i c i n i t y of headlands. Large sheets form i n the S t r a i t o f B e l l e I s l e and the n o r t h e a s t arm of the g u l f and, t o g e t h e r w i t h heavy i c e which enters the s t r a i t from the Labrador coast, chokes up the whole r e g i o n . The amount of i c e which d r i f t s i n t o the g u l f through the s t r a i t i s l a r g e l y c o n t r o l l e d by the t i d a l c u r r e n t s . When the dominance of f l o w Is inward f o r a few days, more i c e enters the g u l f than at other times, but the a c t u a l amount i s f a r l e s s than i t would be I f there were a constant inward c u r r e n t . Some of t h i s pack i c e d r i f t s south ward i n the weak flow to other sect ions of the g u l f where i t may be incorporated i n t o a large i c e f i e l d or s h i f t e d about at the command of wind and wave throughout the w i n t e r . Frequent n o r t h e r l y winds a i d i n d r i v i n g the i c e southward. A few small icebergs and growlers, which have strayed from the Labrador C u r r e n t , may f i n d t h e i r way i n t o the g u l f through the s t r a i t before i t becomes plugged with pack i c e . The west coast of Newfoundland receives the f u l l b e n e f i t of the moderating inf luence of the Gulf of S t . Lawrence. Consequently, the harbours along t h i s coast do not freeze u n t i l January. S t . . George Bay f i l l s with r i v e r ice which seldom becomes cemented Into a f i e l d , but r a t h e r , the f l o e s remain i n motion a l l w i n t e r . Offshore, the northward-flowing eurrent i s e f f e c t i v e i n defending the c o a s t a l area against the i n v a s i o n of i c e from the north u n t i l February. The n o r t h shore of the g u l f remains f a i r l y c l e a r of pack i c e throughout the winter, because of the p r e v a i l i n g northwest winds which c o n t i n u a l l y push the i c e o f f s h o r e , and r i s k y n a v i g a t i o n i s p o s s i b l e . The c e n t r a l part of the g u l f i s covered with pack lee which s h i f t s about c o n s t a n t l y . Leads are r e a d i l y discovered between the f l o e s , but few ships other than i c e - b r e a k e r s attempt n a v i g a t i o n . The general movement of the i c e i n the c e n t r a l g u l f i s from west to east, under the inf luence of the p r e v a i l i n g winds and water c u r r e n t s . Conditions are never s t a t i c because the St . Lawrence R i v e r continues to discharge i c e i n t o the g u l f and new i c e i s forming i n many areas. 35 The i c e Is more.closely packed i n the southern part of the g u l f because of the decreased current and the con finement of the basin by the l a n d . By the middle of January Northumberland S t r a i t and George Bay are usually f i l l e d with c l o s e pack ice and the S t r a i t of Canso i s blocked at the northern entrance. Such a volume of i c e i s swept toward the c o n s t r i c t i o n of the s t r a i t that i t packs s o l i d and freezes i n t o a compact mass which c o n s t i t u t e s a " b r i d g e , " as i t Is commonly c a l l e d . The ef fect of t h i s bridge i s to prevent the i c e i n George Bay from d r i f t i n g i n t o the s t r a i t . This r e s u l t s i n i c e - f r e e condit ions south of Mulgrave and n a v i g a t i o n i n . t h i s s t r e t c h i s p o s s i b l e throughout most of the winter. Pack i c e begins to emerge from the g u l f through Cabot S t r a i t about the middle of January, but I t Is u s u a l l y l i g h t and s c a t t e r e d . In a year of severe condit ions i c e may be found as f a r east as Miquelon I s l a n d i n January, as was the case In 1943. On t h i s o c c a s i o n , January 24, 1943, patches of heavy f i e l d ice were reported at a p o s i t i o n t h i r t y miles southwest of Miquelon. 29 Conversely, i n a year of favourable condit ions, such as 1945, there may be no ice i n the Cabot S t r a i t a r e a . On the average, Cabot S t r a i t i s p a r t l y covered with ice stream i n g out of the g u l f , but i t i s never frozen over from shore to shore. Seldom does the ice extend southward of F l i n t I s l a n d along the east coast of Cape Breton I s l a n d . 29u. S. Treasury Department, Coast Guard, I n t e r n a t l o n - a l Ice Observation and Ice P a t r o l Service i n the North A t l a n t i c Ocean,"Season of 194b, B u l l e t i n NoT 32. Washington, 19*7, P. T 5 ~ " 36 The harbours along the Cape Breton east and south coasts freeze during the second week of January, while those along the south coast of Newfoundland and that of H a l i f a x are u s u a l l y i c e - f r e e throughout the y e a r . These i c e - f r e e harbours are so l o c a t e d that they are protected from the i n v a s i o n of g u l f i c e , and they are c l i m a t i c a l l y favoured i n the r e t a r d a t i o n of l o c a l i c e - f o r m a t i o n . FEBRUARY The main exodus of ice from the g u l f begins i n February. Ice from the c e n t r a l s e c t i o n i s the f i r s t to move o u t . While Ice i s l e a v i n g the g u l f through Cabot S t r a i t , heavy i c e i n the northeast arm continues to d r i f t southward, eventually c l o s i n g on the west coast of Newfoundland as f a r south as the Bay of I s l a n d s . Some of t h i s Ice makes i t s way westward along the north shore. In a d d i t i o n , the St . Lawrence estuary adds i c e to the supply. Consequently, the Cabot S t r a i t outflow Is p a r t l y compensated f o r by Inflows In other areas and by l o c a l f r e e z i n g , but the net r e s u l t Is a l o s s of i c e . G e n e r a l l y , Cabot S t r a i t i s p a r t l y covered with ice c l o s e l y packed on the Cape Breton side and f a i r l y open or s c a t t e r e d on the Newfoundland s i d e . In some y e a r s , as occured i n 1943, the Ice closes In on the Newfoundland coast due to sustained southerly winds, but t h i s Is not the usual con d i t i o n . Eastward of the s t r a i t the i c e i s more open and l i g h t e r and scattered s t r i n g s of i c e frequently extend e a s t ward to the 56th meridian and southward to the 46th p a r a l l e l . 37 O c c a s i o n a l l y , northeast winds cause the i c e to move southwest- ward along the south coast of Nova S c o t i a , b l o c k i n g the harbours. The southern part of the g u l f remains packed with i c e , . much of i t s h i f t i n g , but l i t t l e departing from the area to stream through Gabot S t r a i t . The bays, i n c l u d i n g the Baie de Ghaleur and George Bay, are frozen over completely or are f i l l e d with c l o s e l y packed ice which has been cemented i n t o l a r g e sheets presenting a mosaic appearance. Other areas are covered with ice of a comparable d e s c r i p t i o n , except that there are wide leads between the sheets, p a r t i c u l a r l y i n Northumberland S t r a i t . As e a r l y as February, t h e r e f o r e , the withdrawal of i c e from the g u l f i s inaugurated on a l a r g e s c a l e . T h i s w i t h drawal i s the normal r e s u l t of the c o n t r o l of winds and currents and does not i n d i c a t e that the i c e i s melt ing or breaking up due to m i l d weather. It i s mainly the c e n t r a l area between A n t l c o s t l Is land and Cabot S t r a i t which contributes to the i n i t i a l outflow. SUMMARY The Gulf of St . Lawrence r e c e i v e s i c e from two main sources, the St. Lawrence River and estuary, and the Labrador coast through the S t r a i t of B e l l e I s l e . This i c e from outside mingles with l o c a l l y formed lee c l o s i n g the g u l f to n a v i g a t i o n i n winter. The northeast arm and the western and southern s e c t i o n s of the g u l f are the f i r s t to become i c e - c o v e r e d . Then the c e n t r a l area f i l l s up and the i c e closes the open 3S 8 t r i p along the west coast of Newfoundland. E v e n t u a l l y , the Ice begins to emerge from the g u l f through Cabot S t r a i t . Only the f r i n g e s of the g u l f are frozen s o l i d ; most of the area i s covered with s h i f t i n g pack i c e . The southern p a r t i s the more c l o s e l y packed, but even here leads and pools of open water are found throughout the w i n t e r . CHAPTER IV ICE DISTRIBUTION IN THE BREAKUP SEASON DURING THE YEARS 1940-1952 INCLUSIVE, The general i c e condit ions during the winter months i n d i c a t e that the c l e a r i n g of the g u l f takes place over a long p e r i o d of time and that the i c e leaves p r i m a r i l y through Cabot S t r a i t . With t h i s background the breakup season i s considered. The behaviour of the i c e i n t h i s season of c l e a r i n g can be t r a c e d with some p r e c i s i o n because d e t a i l e d information i s a v a i l a b l e f o r most of the g u l f , except f o r the northeast arm. Although information concerning the breakup i n the northeast arm i s l a c k i n g , i t i s known that the i c e north of a l i n e from Natashquan to the Bay of Islands does not discharge through Cabot S t r a i t , but remains i n the g u l f u n t i l i t has melted. The f o l l o w i n g d e s c r i p t i o n of a c t u a l i c e condit ions i n March and A p r i l of the years 19^0 to 1952, i n c l u s i v e , i s based on information obtained by a e r i a l o b s e r v a t i o n . The data employed were Incomplete concerning March but were d e t a i l e d concerning A p r i l . This d e t a i l e d information i n A p r i l enabled the determination of l i m i t s of the main i c e areas at s p e c i f i e d dates, and these l i m i t s are shown on the maps i n the Appendix. The main i c e areas do not include regions of widely s c a t t e r e d s t r i n g s and small patches of i c e . The graphs which accompany the maps are designed to r e v e a l the temperature c h a r a c t e r i s t i c s of the i c e seasons. S t a t i s t i c s f o r the d i f f e r e n c e from average of the mean 40 monthly temperature were used to achieve these r e s u l t s . 30 In the ease of the years 1940 to 1 9 5 ° , i n c l u s i v e , f i g u r e s f o r twenty-seven meteorological s t a t i o n s were used i n c o n s t r u c t i o n of the graphs, but i n the other two cases, 1951 a n < i 1952, only eighteen s t a t i o n s were u s e d . ^ l The abbreviated l i s t p u b l i s h e d i n the Monthly Weather Map5 2 was employed Instead of that i n the Monthly Record f o r these two y e a r s . The twenty-seven s t a t i o n s are i n d i c a t e d on the map f o l l o w i n g page 4 0 , with a d d i t i o n a l ones which were used as replacements In the event of blanks In the r e c o r d . Those s t a t i o n s used f o r the 1951 and 1952 graphs are u n d e r l i n e d . Because the graphs are intended to show the general temperature c h a r a c t e r i s t i c s of the season over the water area of the g u l f , s t a t i o n s s i t u a t e d on the coast near sea- l e v e l were chosen as most r e p r e s e n t a t i v e . As many s t a t i o n s as p o s s i b l e were Included In order that d e v i a t i o n s from average due to l o c a l causes might be minimized i n company with other s t a t i o n s . In view of the nature of the i c e data a v a i l a b l e , a breakdown of temperatures In various p a r t s of the g u l f was deemed unwarranted, consequently, the s t a t i o n s lose t h e i r l o c a l i d e n t i t y and represent points i n the Gulf of St . partment of Transport , M e t e o r o l o g i c a l D i v i s i o n , Monthly Record (monthly s t a t i s t i c s s e r i e s ) . Toronto, 1940-1950": ^ T h e reduction In number of s tat ions i n these years was n e c e s s i t a t e d because the Monthly Record had not yet reached the p u b l i c a t i o n stage. ^Department of Transport , M e t e o r o l o g i c a l D i v i s i o n . Monthly Weather Map (monthly weather map s t a t i s t i c s s e r i e s ) . Toronto, I95I-I952T Lawrence area as a whole. The h o r i z o n t a l a x i s , zero, Is symbolic of the average temperature of every s t a t i o n i n the g u l f r e g i o n , although the averages may d i f f e r . Each dot represents one s t a t i o n . The d i f f e r e n c e from average at each s t a t i o n i n whole degrees Fahrenheit i s found along the v e r t i c a l a x i s ; each s t a t i o n r e c o r d i n g an average monthly temperature which i s above i t s a l l - t i m e average i s l o c a t e d above the zero l i n e , while each one r e c o r d i n g a below average temperature i s found below the l i n e . I f the f igure f o r a s t a t i o n c o i n c i d e s with the average, to the nearest degree, the dot i s placed on the zero l i n e . I t must be emphasized that t h i s chapter i s p r i m a r i l y a p r e s e n t a t i o n of data. Further i n t e r p r e t a t i o n of the ma t e r i a l w i l l be found In f o l l o w i n g s e c t i o n s . The maps f o r each season are designed to accompany the text and should be consulted i n conjunction with i t . SEASON OF 1940 During March there was a considerable area of open water i n the g u l f , p a r t i c u l a r l y i n the c e n t r a l s e c t i o n along the steamer track.23 A great deal of c lose pack i c e lay i n the southern h a l f , although there were pools of open water and numerous l e a d s . The exodus through Gabot S t r a i t was i n progress. ^The "steamer t r a c k " i s the d i r e c t route from Gabot S t r a i t to the St . Lawrence estuary south of A n t i c o s t i I s l a n d which i s fol lowed by most ocean v e s s e l s . 42 By early A p r i l the i c e was melt ing and breaking up i n the western part of the g u l f . The open channel along the steamer t r a c k had widened, but the passage through Cabot S t r a i t on the Newfoundland side remained c o n s t r i c t e d . The Bale de Ghaleur was c l e a r i n g along the northern s i d e . Northumberland S t r a i t and the east coast of Prince Edward Is land were open; s i m i l a r l y , there was open water In the v i c i n i t y of the Magdalen I s l a n d s . The Ice was confined, e s s e n t i a l l y , to the eastern h a l f of the g u l f at the middle of A p r i l . The bulk of the Ice had withdrawn from the g u l f by A p r i l 25 when the main f i e l d lay off the east and south coasts of Cape Breton I s l a n d . Shortly a f t e r the middle of the month the route through the S t r a i t of Ganso, George Bay, and v i a East Point became open. Some s c a t t e r e d i c e which, c o n s t i t u t e d a danger to n a v i g a t i o n remained i n Northumberland S t r a i t u n t i l the end of A p r i l . The f i e l d off the east coast of Cape Breton covered a r e l a t i v e l y l a r g e area d u r i n g much of A p r i l and reached along the south coast as f a r as St. E s p r i t , but i t shrank q u i c k l y i n the l a s t week, r e v e a l i n g open water across the f u l l width of Cabot S t r a i t . Gn the whole, ice condit ions were not severe during t h i s season of 194-0. The breakup was w e l l under way i n March and was a c c e l e r a t e d during A p r i l . The c l e a r i n g proceeded from west to east and the l a s t remaining ice of any conse quence was found off the Gape Breton coast. The graphs Indicate that the season was warmer than average, i n s p i t e of the f a c t that two months, November and A p r i l , were d e f i n i t e l y below normal. March was nearer the average than any of the other months. The m i l d winter assured that ice condit ions would not be severe by preventing the ice from becoming unduly t h i c k or extensive. SEASON OF 1941 Close pack ice covered about h a l f of the g u l f i n March, 1941, although there were some large patches of open water, e s p e c i a l l y between A n t i c o s t l I s l a n d and Gaspe and i n the southern part of the g u l f . The Cabot S t r a i t region was choked up w i t h close pack i c e which extended a great distance southeastward. The western part of the g u l f was mainly c l e a r by A p r i l 5, except f o r i c e In.the Baie de Chaleur and t h i s i c e was moving out q u i c k l y . As i n 1940, open water was found along the east coast of Prince Edward I s l a n d . The Ice had moved to the eastern side of the g u l f where I t covered the steamer t r a c k and completely f i l l e d Cabot S t r a i t . Eastward and southward of the s t r a i t the f i e l d was unusually extensive because the quantity of i c e i n the g u l f was great and the c l e a r i n g took place r a p i d l y . The i c e was packed on the Cape Breton east coast. By the middle of A p r i l the i c e had receded from the c e n t r a l s e c t i o n , opening a narrow passage through Cabot S t r a i t and along the steamer r o u t e . Along the east coast of Gape Breton the Ice had moved offshore w i t h westerly winds, but the f i e l d remained extensive. Northumberland.Strait , George Bay, and the S t r a i t of Ganso opened d u r i n g the t h i r d week of the month, although i c e clung to the west coast of Gape Breton u n t i l nearly the end of A p r i l . The f i e l d outside Gabot S t r a i t , which was s t i l l offshore, had contracted by A p r i l 25 and disappeared s h o r t l y a f t e r . Between Heath Point and Cape S t . George the ice l i n g e r e d u n t i l e a r l y May. The breakup was w e l l advanced by the end of the f i r s t week i n A p r i l i n t h i s season and the whole area was p r a c t i c a l l y c l e a r by May 1. Considering the quantity of ice which had to be expel led from the g u l f , more than i n l$HO, the breakup was reasonably swift and fol lowed a normal p a t t e r n . The ice made i t s way from west to east and passed through Cabot S t r a i t i n the same manner as i t had done i n 19^0, except that the s t r a i t and the steamer t r a c k were i c e - c o v e r e d u n t i l a l a t e r date and the greater volume of i c e was spread over a wider area beyond the s t r a i t . > Temperatures i n the g u l f area were near average In November, but were d e f i n i t e l y below average i n December and January. February temperatures were remarkably h i g h , while those of March and A p r i l were nearer normal. The fact that the i c e was heavier than i n 1940 was probably due to the lower temperatures i n December and January. SEASON OF 1942 The i c e was l e s s extensive during March, 194-2, than i t had been the year before. Frequent northerly winds throughout March and A p r i l s h i f t e d the i c e to the southern p a r t of the g u l f . As i n previous y e a r s , the Bale de Ghaleur began opening f i r s t along the northern s i d e . I t appears 4 5 l i k e l y that t h i s p a t t e r n of c l e a r i n g i s c h i e f l y determined by the i s l a n d s which narrow the mouth of the bay. Open water extended southward from the Baie de Ghaleur i n t o Northumberland S t r a i t . The steamer t r a c k was c l e a r , u n l i k e the c o n d i t i o n i n 1941, and there was an open route through Cabot S t r a i t on the Newfoundland s i d e . Beyond the s t r a i t the n o r t h e r l y winds had c a r r i e d the i c e f a r southward along the south coast of - Nova S c o t i a . The southerly movement of the i c e continued through out A p r i l under the Influence of n o r t h e r l y winds. A shore, l e a d along the north coast of Prince Edward I s l a n d was pinched out by the middle of the month. The Improvement i n the southern sect ion where the ice f i e l d s had contracted by A p r i l 15 was p a r a l l e l e d by the i n v a s i o n of an extensive f i e l d from the n o r t h which covered, a large part of the steamer t r a c k . A f t e r the middle of A p r i l the ice was slow In rounding Cape North and tended to remain i n the r e g i o n of George Bay. . During l a t e A p r i l the f i e l d south of A n t l c o s t i I s l a n d s t i l l c o n s t i t u t e d a hazard. Although George Bay and the S t r a i t of Ganso had been c l e a r on A p r i l 25, c lose pack i c e was d r i f t e d i n t o the bay by winds a few days l a t e r , c l o s i n g n a v i g a t i o n u n t i l the i c e withdrew on May '3 and eventually made i t s way up the west coast of Gape Breton and around Cape North. The south coast of Cape Breton was c l e a r throughout A p r i l because there were no southerly winds powerful enough to push the i c e on shore. 4-6 At the beginning of A p r i l the breakup was s u f f i c i e n t l y advanced to indicate an early opening of a l l navigation routes. Much of the gulf was open and the i c e , confined to the southern section, was loosely d i s t r i b u t e d over a wide area. However, the flow of Ice through Cabot S t r a i t was r e s t r i c t e d by northerly winds and the ice accumulated along the west coast of Gape Breton. In addition, a large f i e l d encroached on the steamer track south of A n t i c o s t l Island and dispersed very slowly. As a re s u l t , the pattern of breakup d i f f e r e d from that of the previous two years i n the fa c t that the ice d i d not d r i f t f r e e l y from west to east, taking advantage of the f u l l width of Cabot S t r a i t as an e x i t . Rather, i t stagnated i n the southern section and clogged the George Bay-Strait of Ganso area u n t i l early May. In respect to temperature, November and January were the only months which were d i s t i n c t l y below average. The rest of the months were warmer than normal, March In p a r t i c u l a r when temperatures ranged from three to ten degrees above average. The December, March, and A p r i l temperatures were higher than i n 194-1 which accounted f o r the l i g h t e r ice conditions experienced early i n the season. SEASON OP 194-3 Most of the gulf was ice-covered throughout March. In many areas the ice was closely packed, especially i n the Bale de Chaleur, around Gape Breton Island, and i n Gabot S t r a i t . Outside the s t r a i t the southward and eastward extension of the ice was greater during the l a t t e r half of March than during the f i r s t h a l f . This condition was a normal r e f l e c t i o n of the acceleration of the clearing during the breakup season. Because westerly winds prevented the ice from c l o s i n g i n on the south coast of Cape Breton, i t remained clear. Early i n A p r i l there was s t i l l a great deal of open pack Ice i n the gulf. The steamer track was unnavigable, although i t was opening south of A n t i c o s t i Island. L i t t l e improvement had taken place in the Baie de Chaleur. East of the Magdalen Islands the ice was very open, but Cabot S t r a i t was s t i l l p a r t l y f i l l e d with close pack Ice. With frequent southerly winds the ice was withdrawing northward from George Bay, leaving the S t r a i t of Canso and the bay open. This northward movement of the ice continued through A p r i l and l e d to the early clearing of the southeastern section of the gulf. Close pack ice remained i n central regions and along the steamer track, however, u n t i l . l a t e i n A p r i l . The fact that the ice moved northward blocking the mouth of the Bale de Chaleur was responsible f o r the retarded breakup of the bay. Gabot S t r a i t began to open f i r s t on the Gape Breton side as the ice receded from the coast. This unusual pattern of c l e a r i n g was caused mainly by southerly winds. The gulf cleared rapidly during the l a s t few days of A p r i l and the steamer track was navigable throughout on A p r i l 30. Some Ice remained u n t i l early May In the Baie de Chaleur and off the west coast of Newfoundland. . The' 1943 breakup followed quite a d i f f e r e n t pattern from those of the preceding three years. In t h i s season ice i n the main body of the gulf was more abundant. It cleared 4g f i r s t i n the area east of G-aspe' P e n i n s u l a , then i n the south eastern part of the g u l f , and l a s t of a l l , i n the c e n t r a l s e c t i o n along the steamer route. The main c o n t r i b u t i n g f a c t o r i n t h i s withdrawal was the frequent occurrence of southerly winds. In the matter of temperature during the i c e season, i t i s apparent that below normal condit ions p r e v a i l e d i n every month except November and February. Only February.was decidedly warmer than average, while December, January, March, and A p r i l were considerably c o l d e r than average. These lower temperatures l e d to the occurrence In t h i s season of wide spread, heavy i c e , much of which was c l o s e l y packed. SEASON OF 1944 The breakup proceeded with r a p i d i t y during March. Although the i c e was f a i r l y extensive early In the month, s trong northwest and west winds opened up the i c e throughout the g u l f and c a r r i e d i t eastward to feed a broad stream of i c e d r i f t i n g through Gabot S t r a i t . A narrow passage remained open on the Newfoundland side during most of the month, probably owing to the inward c u r r e n t . The southward and e a s t ward l i m i t s of the i c e outside the s t r a i t approximated those of A p r i l 5« * n l a t e March the eastern part of the steamer t r a c k c l e a r e d and the ice receded from the whole west coast of the g u l f , except i n the Bale de Chaleur. This r a p i d d i s p e r s a l may be a t t r i b u t e d , c h i e f l y , to sustained northwest winds. By A p r i l 5 the i c e had withdrawn to the Cape Breton I s l a n d r e g i o n . Close pack i c e i n Northumberland S t r a i t and George Bay blocked the route through the S t r a i t of Canso and reached up the west coast of Cape Breton. As i n 1940 and 1941, the east coast of Prince Edward I s l a n d was open. This evidence supports the conclusion that southeast c o a s t a l areas are c l e a r e d r e a d i l y by northwest winds. Gabot S t r a i t remained p a r t l y i c e - c o v e r e d and the i c e i n the d i s p e r s a l area was unusually extensive as a r e s u l t of the presence of a l a r g e quanti ty of i c e which l e f t the g u l f during March. Along the Cape Breton east coast the ice was i n s h o r e , f i l l i n g Sydney harbour. Northumberland S t r a i t had l a r g e l y c l e a r e d by the middle of A p r i l . Southwest winds moved the ice i n George Bay northward on A p r i l 15, rendering the route navigable, but n o r t h e r l y winds caused i t to invade the bay again on A p r i l 17, o b s t r u c t i n g the passage. In the Baie de Chaleur the Ice had opened and was d i s p e r s i n g , i n spite of the fact that i t s l i m i t s had changed l i t t l e since A p r i l 5. The f i e l d i n Cabot S t r a i t and beyond was d i m i n i s h i n g and had receded from.the Gape Breton coast with southwest winds. As a r e s u l t , Sydney harbour c l e a r e d . Most of the g u l f was c l e a r by A p r i l 25 with the exception of Ice i n George Bay and the S t r a i t of Canso, which prevented navigat ion u n t i l A p r i l 27, and along the west coast of Gape Breton. Some f i e l d s of Ice remained offshore beyond C a b o t . S t r a i t , but these were d i s i n t e g r a t i n g r a p i d l y . 50 The p a t t e r n of breakup i n 1944 resembled that of 194-2 i n c e r t a i n r e s p e c t s . There was a wide area of open water on A p r i l 5 i n each case, but the c o n d i t i o n s during March were d i f f e r e n t . In the one i n s t a n c e , 1942, much open water was v i s i b l e i n March, while i n the o t h e r , 1944, the i c e had been extensive but c leared r a p i d l y . In both cases George Bay was invaded by Ice at a l a t e date owing to n o r t h e r l y winds. The temperatures of the autumn were high enough to r e t a r d ice formation. December and January were i n c o n t r a s t ; the f i r s t was w e l l below average and the second was well above. February temperatures were near normal, but those of March and A p r i l were lower. The f a c t that the Ice condit ions were not so severe as i n the year before would suggest that the temperatures were higher, which was the case. SEASON OF 1945 The season of 1945 was s i n g u l a r i n i t s paucity of i c e , owing to m i l d winter temperatures. During March the i c e which d i d e x i s t was segregated i n the southern part of the g u l f . George Bay was f i l l e d with c l o s e pack i c e which ex tended up the west coast of Gape Breton I s l a n d , elsewhere, the i c e was f a i r l y open. The flow of Ice through Cabot S t r a i t was very l i m i t e d i n amount and was confined to a narrow b e l t on the Cape Breton s i d e . The s t r a i t was never c l o s e d during the month. In the d i s p e r s a l r e g i o n the ice f i e l d reached i t s greatest extent d u r i n g early March, then i t diminished r a p i d l y during the l a t t e r part of the. month. 51 T h i s f i e l d was of l e s s e r dimensions than those of previous y e a r s . Only on one o c c a s i o n , at the middle of March, d i d the i c e move onshore along the south coast of Cape Breton i n the v i c i n i t y of Louisburg, but t h i s i n c u r s i o n , caused by easterly winds, was s h o r t - l i v e d . The g u l f was p r a c t i c a l l y c l e a r by the end of the f i r s t week i n A p r i l . The only i c e remaining was i n the Bale-de Chaleur, around the Magdalen I s l a n d s , i n George Bay, and along the west coast of Gape Breton. Most of t h i s i c e moved out q u i c k l y , rendering the route through the S t r a i t of Canso navigable by A p r i l 6. The f i e l d o f f the Cape Breton east coast had almost completely d i s s i p a t e d and l e f t only a s t r i p of ice near shore. The whole season of 1945 w a s c h a r a c t e r i z e d by m i l d i c e c o n d i t i o n s . Ice was l a t e In forming In the f a l l and was never very extensive during the winter, consequently, the breakup and f i n a l c l e a r i n g occured remarkably e a r l y . The p a t t e r n of , breakup was s i m i l a r to that of 1944, although the amount of i c e Involved was much l e s s . The i c e departed from the g u l f v i a a route l y i n g on the southern side of Gabot S t r a i t . Inside the g u l f i t l i n g e r e d i n three p a r t i c u l a r areas a l i t t l e longer than i n others, the Bale de Chaleur, the v i c i n i t y of the Magdalen Is lands, and the George Bay r e g i o n . E x c e p t i o n a l l y h i g h temperatures throughout the season were mainly responsible f o r these clement i c e c o n d i t i o n s . A l l months, except December, were considerably warmer, than average and even December was s l i g h t l y warmer than normal.. SEASON OF 1946 L i t t l e information was a v a i l a b l e concerning ice con d i t i o n s i n March. I t i s e s t a b l i s h e d that there were wide areas of open water i n many sections of the g u l f throughout the month. P r e v a i l i n g northwest winds during March l e d to the removal of a considerable quantity of i c e through Cabot S t r a i t . . The steamer t r a c k was almost c l e a r at the end of the month. By A p r i l 5 the t r a c k was navigable with patches and s t r i n g s of loose ice and the western part of the g u l f was c l e a r . Northumberland S t r a i t was navigable from the western entrance to P i c t o u I s l a n d . The majority of the i c e i n the g u l f lay i n the southeastern s e c t i o n along the n o r t h coast of Prince Edward Island and the west coast of Cape Breton I s l a n d . George Bay and the S t r a i t of Canso were unnavigable. In Cabot S t r a i t a narrow s t r i p of i c e was pressed c lose against the l a n d and the ice was inshore along the Cape Breton east coast . The i c e f i e l d beyond the s t r a i t reached f a r southward, but i t s eastward extent was more l i m i t e d . Frequent northeast, winds during A p r i l undoubtedly caused t h i s southward d r i f t of the i c e . The f i e l d s gradually diminished throughout the r e s t of A p r i l without any d r a s t i c a l t e r a t i o n s of t h e i r p o s i t i o n s , although i n m i d - A p r i l a tongue of i c e was thrust southward along the Nova S c o t i a south coast by e a s t e r l y winds. George Bay c l e a r e d i n the l a t t e r h a l f of the month, enabling the commencement of navigation on that r o u t e . It was not u n t i l the l a s t week of A p r i l that the i c e i n the f i e l d off the west coast of Cape Breton opened up and rounded Cape North to d i s s i p a t e "beyond Gabot S t r a i t . Only a few patches of Ice remained by May 1. - During the winter of 1946 a moderate quantity of i c e appeared i n the g u l f , but r a p i d c l e a r i n g occurred i n March. Throughout A p r i l the withdrawal of the i c e proceeded more s l o w l y , i n a manner s i m i l a r to i t s behaviour i n 1942. In both cases northeast winds p r e v a i l e d during A p r i l which drove the i c e southward and tended to discourage i t s free movement through Gabot S t r a i t . The f i r s t four months of the 1946 ice season were c h a r a c t e r i z e d by temperatures near the average. March temperatures were somewhat higher than normal and A p r i l temperatures were s l i g h t l y lower. The s i t u a t i o n with regard to i c e was not i n c o n s i s t e n t with these data. The near aver age temperature condit ions i n d i c a t e that t h i s p a r t i c u l a r season may have experienced near average amounts of i c e . SEASON OP 1947 The i c e i n the g u l f during March was more extensive than i t was the year before. Although there were few areas of open water, one of which lay along the east coast of P r i n c e Edward Is land, the Ice opened up a great d e a l In March, e s p e c i a l l y along the steamer t r a c k . The flow through Cabot S t r a i t was not excessive and the i c e f i e l d beyond the s t r a i t was unusually contracted. E a r l y i n A p r i l a large area i n the g u l f was s t i l l i c e - c o v e r e d , but much of the i c e was open and s c a t t e r e d . As was customary i n former y e a r s , the Baie de Chaleur c l e a r e d f i r s t along the northern s i d e . The steamer t r a c k and a s t r i p i n the southwestern part of the g u l f , i n c l u d i n g Northumberland S t r a i t , c l e a r e d during the second week of A p r i l . The route through the S t r a i t of Canso and George Bay a l s o became n a v i gable at t h i s time. In tne d i s p e r s a l region the f i e l d was very l i m i t e d i n extent and a shore l e a d e x i s t e d along the northeast coast of Cape Breton. Occasional periods of southerly winds were e f f e c t i v e i n c l e a r i n g the southern part of the g u l f r e a d i l y and i n maintaining a shore l e a d along the east coast of Gape B r e t o n . The c e n t r a l s e c t i o n of the g u l f between the Magdalen Islands and Prince Edward Island where the i c e was scattered c l e a r e d a f t e r A p r i l 15. Cabot S t r a i t was e s s e n t i a l l y c l e a r at t h i s time. Toward the end of the month the f i e l d off the Cape Breton west coast broke up and began moving r a p i d l y around Cape North. The f i e l d off the east coast r e t r e a t e d from shore and the i c e dispersed s h o r t l y afterwards. North of the steamer t r a c k some i c e remained u n t i l May. The breakup p a t t e r n of 1947 D o r e a c lose resemblance to that of 1941. The Ice was reasonably extensive and heavy during March. I t c l e a r e d f i r s t i n the western part of the g u l f , along the steamer r o u t e , and i n Northumberland S t r a i t and George Bay, then i n the c e n t r a l a r e a , and l a s t of a l l , a long the west coast of Gape Breton, north of the steamer t r a c k , and i n the d i s p e r s a l r e g i o n . A s i m i l a r i t y was a l s o evident i n the i c e season temperatures of the two years. February was unusually warm i n both years. The f i r s t three months of the 19^ 7 season were c o l d e r than normal and A p r i l was c o l d e r s t i l l . March, l i k e February, was above average, although the ice was f a i r l y extensive i n s p i t e of i t , thus i n d i c a t i n g that low early winter temperatures are c r i t i c a l i n i c e formation. SEASON OF 19^8 At the middle of March the whole g u l f was i c e - c o v e r e d . The i c e was more c l o s e l y packed In the southern p a r t , but there was l i t t l e open water anywhere. Beyond Cabot S t r a i t the i c e was spread over a tremendous a r e a . C l e a r i n g proceeded r a p i d l y d u r i n g the l a t t e r h a l f of the month with strong westerly winds and s e v e r a l areas opened s u f f i c i e n t l y to r e v e a l open water, p a r t i c u l a r l y along the steamer t r a c k . A very narrow shore l e a d e x i s t e d i n Cabot S t r a i t off Gape Ray and Cape A n g u i l l e . The l i m i t s of the f i e l d i n the d i s p e r s a l r e g i o n had receded to the p o s i t i o n s where they remained throughout A p r i l . The speedy withdrawal of the i c e frorm west to east continued i n A p r i l aided by strong northwesterly g a l e s . Much of the western part of the g u l f was c l e a r e a r l y i n the month, except f o r the Bale de Ghaleur which was c l o s e l y packed on the southern s i d e . The eastern part of the steamer t r a c k was s t i l l c l o s e d by i c e , although the narrow shore lead remained along the Newfoundland coast. S i m i l a r l y , the Cape Breton east coast was c l e a r throughout the month. 56 Northumberland S t r a i t and George Bay were opening up, but were not c l e a r u n t i l the t h i r d week of A p r i l . The S t r a i t of Ganso which had been c l e a r on A p r i l 5 w a s admitting a flow of s c a t t e r e d i c e that impeded n a v i g a t i o n . Toward the end of A p r i l the i c e was mainly confined to the Gape Breton area. Gabot S t r a i t was l a r g e l y i c e - c o v e r e d and the f i e l d beyond occupied an area as great as that on A p r i l 15. The i c e , which had been offshore throughout A p r i l , was d r i v e n on the coast on A p r i l 27 by strong northeast winds, l e a v i n g Cabot S t r a i t e s s e n t i a l l y open. Here the f i e l d remained u n t i l I t loosened up and d i s p e r s e d a f t e r Hay 9 with westerly winds. Sydney harbour was completely blocked u n t i l t h i s date. The l a r g e quantity of ice i n the g u l f e a r l y i n the breakup season c l e a r e d r a p i d l y , g a i n i n g e x i t through Gabot S t r a i t . I t occupied most of the s t r a i t during*March and A p r i l . The i c e withdrew from west to east i n a normal manner and vacated the George Bay area before the Gape Breton north and east c o a s t a l areas. However, the i c e i n t h i s last-mentioned r e g i o n moved onshore at the end of A p r i l and d i d not c l e a r u n t i l the second week of May. E s s e n t i a l l y , the breakup r e sembled that of 1941, except that the Cape Breton region was encased by i c e u n t i l an e x c e p t i o n a l l y l a t e date. Temperatures were above average i n November and January, near average i n December, and d i s t i n c t l y below average i n February, March, and A p r i l . Although the early winter temperatures were s l i g h t l y above average, there was 57 a great amount of heavy i c e i n t h i s season. The importance of low e a r l y winter temperatures i s reduced by t h i s f a c t . SEASON OF 1949 In the season of I949 the i c e was somewhat l i g h t e r than the year before, n e v e r t h e l e s s , It covered a wide a r e a . The majority of the i c e was i n s i d e the g u l f on the March 15; the steamer t r a c k east of the B i r d Rocks as w e l l as Cabot S t r a i t was c l e a r , and beyond the s t r a i t there were a few patches of loose i c e only. By March 25 the ice had moved eastward under the influence of northwest winds, covering the steamer t r a c k and a l l but c l o s i n g Cabot S t r a i t , except f o r a shore l e a d around Cape Ray. I t had d r i f t e d along the Cape Breton east coast to S c a t a r i . Accompanying t h i s movement was a withdrawal of i c e from the Gaspe coast. The c l e a r i n g of the Baie de Chaleur was In progress, w i t h the i c e moving out of the northern h a l f . Other parts of the g u l f remained I c e - covered. Great improvement had taken place by A p r i l 5 ' T n e most notable was the r e t r e a t of the ice from the western part of the g u l f and the opening of the steamer t r a c k . Although the steamer route was navigable, there was considerable , s c a t t e r e d and open i c e i n the area. Gabot S t r a i t I t s e l f was f a i r l y open, but the f i e l d outside the s t r a i t had been d r i v e n onshore along the east and south coasts of Gape Breton by n o r t h e r l y winds. By the middle of A p r i l the Baie de Chaleur was c l e a r and most of Northumberland S t r a i t was open, while scattered i c e was strewn over the steamer t r a c k , although i t was n a v i gable. George Bay and the west coast of Gape Breton were s t i l l i c e - c o v e r e d , but were s w i f t l y c l e a r i n g . Along the Gape Breton south coast the ice had moved offshore. A l l these areas were c l e a r by the end of the t h i r d week of A p r i l . F i n a l l y , n o r t h e r l y gales on A p r i l 25 broke up the e n t i r e f i e l d l o c a t e d o f f the east- coast of Gape Breton and scattered the i c e widely. The i c e season was not severe i n 1949. Once the c l e a r i n g began i n earnest a f t e r March 15 i t proceeded speedily and i n an o r d e r l y f a s h i o n . Moving from west to east , the iee departed from the g u l f through Gabot S t r a i t and l e f t behind few traces a f t e r A p r i l 25. This season may be compared with 1940, f o r the breakup followed a s i m i l a r p a t t e r n , although the ice was much l i g h t e r i n 19^9. The l i g h t ice condit ions were due, i n p a r t , to remarkably h i g h temperatures. A l l months except February were four or f i v e degrees above average at many s t a t i o n s . February temperatures were nearer average. SEASON OF 1950 During March, 1950, the flow of i c e through Cabot S t r a i t was i n considerable volume. Several areas were open toward the end of the month; among them were the western part of the steamer t r a c k and the region from the Bale de Ghaleur to Northumberland S t r a i t . The r e s t of the g u l f was i c e - covered. Gabot S t r a i t was f i l l e d with i c e and the f i e l d outside was unusually extensive because of the abundance of i c e and the moderately r a p i d rate of c l e a r i n g during March. 59 The steamer t r a c k was e s s e n t i a l l y c l e a r hy A p r i l 5* except f o r a tongue of i c e which was thrust across i t near Gape A n g u i l l e by n o r t h e r l y winds. Frequent n o r t h e r l y winds were packing the i c e i n the southern part of the g u l f . The Baie de Ghaleur was opening along the northern side and Northumberland S t r a i t was p a r t l y c l e a r . D r i f t i c e was strewn over much of the c e n t r a l s e c t i o n of the g u l f . In Gabot S t r a i t the i c e occupied only the southern h a l f , but the f i e l d i n the d i s p e r s a l r e g i o n remained extensive. Although the ice had been offshore along the east coast of Gape Breton on A p r i l 3> i t moved onshore a few days l a t e r . By A p r i l 15 the Ice was compacted In the southeastern s e c t i o n of the g u l f and In the d i s p e r s a l r e g i o n , with the exception of a broad band of ice which had been d r i f t e d southward across the steamer route by the n o r t h e r l y winds. The Baie de Ghaleur had l a r g e l y c l e a r e d and was navigable to Dalhousle. George Bay, however, was f u l l of i c e and the S t r a i t of Ganso was d i s c h a r g i n g i c e southward i n t o the A t l a n t i c . Glose pack Ice covered the p a r t of Gabot S t r a i t between Cape North and St. Paul I s l a n d . The ice was s t i l l c l o s e inshore along the east coast of Cape Breton and, i n a d d i t i o n , the f i e l d had moved a great distance southward and occupied the south c o a s t a l area. Toward the end of the month n o r t h e r l y winds h e l d the i c e In the southeastern part of the g u l f , r e s t r i c t i n g the flow around Gape North. The steamer t r a c k had c l e a r e d and the f i e l d beyond Cabot S t r a i t had diminished, but a great d e a l 6o of lee remained i n s i d e the g u l f which must eventually a r r i v e i n the area of d i s p e r s a l . The c l e a r i n g of the southeastern part of the g u l f was g r a d u a l ; the S t r a i t of Canso was not e n t i r e l y c l e a r f o r n a v i g a t i o n u n t i l May 7 and the i c e l i n g e r e d along the Gape Breton coast u n t i l the middle of May. Once around Gape North the i c e spread over a wide area, no longer c o n s t i t u t i n g a danger to n a v i g a t i o n . The ice i n t h i s season was reasonably extensive and heavy. The p a t t e r n of c l e a r i n g during A p r i l was more from n o r t h to south than from west to e a s t . Northerly winds were mainly responsible f o r the accumulation of the i c e i n the southeastern p o r t i o n of the g u l f . These condit ions resembled those of 19 -^2 when the i c e seemed to stagnate i n t h i s a r e a , but the s i t u a t i o n was worse i n 1950 because the i c e was more abundant and the f i n a l c l e a r i n g was postponed even l o n g e r . Concerning temperature, December and January were the only months which were warmer than average. The l a t t e r p a r t of the season was c o l d e r , with February and March much c o l d e r than average. These condit ions approximated those of 19kg and l e n d weight to the a s s e r t i o n that l a t e winter temperatures which are w e l l below average may l e a d to an abundance of i c e . SEASON OF I95I The season of 1951 displayed a most p e c u l i a r i r r e g u l a r i t y . Throughout the season the i c e was segregated i n the western part of the g u l f . At the end of the f i r s t week i n 61 March there was p r a c t i c a l l y no i c e east of the 62nd meridian. West of t h i s meridian the i c e was open i n the c e n t r a l s e c t i o n and c l o s e l y packed near shore. As March progressed the i c e dispersed i n the offshore areas, while i t remained c l o s e l y packed along the New Brunswick coast, i n Northumberland S t r a i t , and along the north shore of Prince Edward I s l a n d . Strong and sustained northeast and east winds through March and A p r i l w e r e . d i r e c t l y responsible f o r the accumulation of ice along the west shore of the g u l f . By A p r i l 5 the f i e l d north of Prince Edward I s l a n d was disappearing and the Bale de Ghaleur was opening along the northern s i d e . Most of Northumberland S t r a i t was c l e a r . A southward movement of the Ice took place i n the second week of A p r i l when the wind became more n o r t h e r l y , l e a v i n g the r e g i o n off the mouth of the Baie de Ghaleur c l e a r of Ice. On A p r i l 16 b r i s k westerly winds f i n a l l y loosened up a l l the i c e i n the southern part of the g u l f and i t d r i f t e d seaward. By A p r i l 25 the only Ice o b s t r u c t i n g navigat ion was l o c a t e d In Northumberland S t r a i t , but i t d i s s i p a t e d before the end of the month. The pattern of breakup i n 1951 was not p a r a l l e l e d by any of the previous ten seasons. The i c e condit ions were as l e n i e n t i n t h i s season as they were i n 19^5. The main d i s t i n c t i o n between the seasons lay i n the fact that the i c e which entered the g u l f from the St . Lawrence River was packed along the New Brunswick coast by e a s t e r l y winds, r a t h e r than c a r r i e d through to Gabot S t r a i t by westerly winds. The concentrat ion of ice along t h i s coast had.the a d d i t i o n a l '62 effect of r e t a r d i n g the breakup of the Bale de Ghaleur. When the ice d i s p e r s e d i t s c a t t e r e d widely and d i d not hinder n a v i g a t i o n i n other areas. The routes through Gabot S t r a i t and the S t r a i t of Canso were c l e a r throughout March and A p r i l . The i c e season was remarkably m i l d , perhaps the mildest of the years examined. Temperatures were, several degrees above average i n every month. A great part of the g u l f was i c e - f r e e throughout the season, and i t i s d e f i n i t e t h a t 1 t h e i c e was e x c e p t i o n a l l y l i g h t . SEASON OP 1952 The whole c e n t r a l sect ion of the gulf was c l e a r by the middle of March and the main i c e area was i n the southern p o r t i o n . Much of t h i s area was covered with close pack i c e . Northerly winds through February and March d r i f t e d the i c e southward. The fl'ow of i c e through Gabot S t r a i t increased toward the end of March with the s t r a i t h a l f covered, but the i c e was of l i m i t e d extent beyond. In e a r l y A p r i l the Bale de Ghaleur continued to c l e a r along the northern s i d e , and Northumberland S t r a i t and G-eorge Bay were beginning to open up. Most of the i c e had r e t r e a t e d even f u r t h e r southward. Off the east coast of Gape Breton the i c e had spread over a l a r g e r area and had moved onshore, also encroaching on the south coast. Because the winds during A p r i l were l i g h t and v a r i a b l e i n d i r e c t i o n , they d i d not s h i f t the i c e to other regions or encourage i t s quick withdrawal from the g u l f . The c l e a r i n g progressed g r a d u a l l y , r e s u l t i n g i n more areas of open water by the middle of the month, e s p e c i a l l y around Prince Edward I s l a n d . Cabot S t r a i t was mainly open and the i c e beyond had receded from the Gape Breton coast. By the end of A p r i l the i c e f i e l d s had shrunken, but c o n s i d e r able i c e remained as a formidable obstacle to n a v i g a t i o n . Close pack i c e covered the eastern h a l f of George Bay and much of the S t r a i t of Canso, as w e l l as the Gape Breton west c o a s t a l r e g i o n . The d r i f t i c e i n the eastern h a l f of Northumberland S t r a i t prevented n a v i g a t i o n v i a t h i s r o u t e . Strong northwest winds on A p r i l 24 were e f f e c t i v e i n c l e a r i n g the east and south coasts of Gape B r e t o n , l e a v i n g only a few s c a t t e r e d patches and s t r i n g s . George Bay and the S t r a i t of Canso were not c l e a r u n t i l May 3 and some Ice l i n g e r e d In Northumberland S t r a i t f o r another week. The breakup of 1952 was s i m i l a r to that of 1942, ten years e a r l i e r . In both years the g u l f began c l e a r i n g at an early date, but ice remained i n the southern sect ions u n t i l e a r l y May, b l o c k i n g the S t r a i t of Canso route. The r e t a r d a t i o n of the breakup was to be a t t r i b u t e d p r i m a r i l y to n o r t h e r l y winds, which packed the i c e i n the south, and to the l a c k of sustained periods of southerly or westerly winds, which would have a c c e l e r a t e d the exodus. The records of temperature i n d i c a t e that the season was above average i n t h i s respect . November and December were nearer average than the other four months which were above. The ice was more extensive than i n 1951, °ut the i c e season was s t i l l l i g h t e r than normal. CHAPTER V THE NATURE OF THE BREAKUP AND THE DETERMINING FACTORS PATTERNS AND RATES OF BREAKUP It Is apparent from the examination of the maps of i c e c o n d i t i o n s In the Gulf of St . Lawrence that the p a t t e r n and rate of breakup v a r i e s immensely from year to y e a r . Never t h e l e s s , the fundamental d r i f t of the ice i s from west to east. Cabot S t r a i t , c o n s t i t u t i n g the main o u t l e t from the g u l f , Is the d e s t i n a t i o n of most of the i c e , except f o r that i n the northeast arm. Deviations of the i c e from the most d i r e c t route to Cabot S t r a i t , which are caused by numerous f a c t o r s , are r e s p o n s i b l e f o r the d i f f e r e n t patterns and r a t e s of breakup. In Most years there are c e r t a i n areas which become free of i c e before o t h e r s . A t r i a n g u l a r region o f f the south coast of Newfoundland, with the apex at Cape Ray, i s g e n e r a l l y i c e - f r e e throughout the year and a passage around Cape Ray and Cape A n g u l l l e Is open most of the t ime. The c e n t r a l part of the g u l f northwest of Gabot S t r a i t discharges i c e i n January or February, but i t continues to r e c e i v e more from other sections and, as a r e s u l t , i t i s seldom the f i r s t area to become c l e a r , although i t c l e a r s before the southern p a r t . The s t r e t c h south of A n t i c o s t i I s l a n d appears to open f i r s t , then the western s e c t i o n and the steamer r o u t e , and f i n a l l y , the southeastern s e c t i o n and the d i s p e r s a l r e g i o n . 6 5 While i c e remains i n the Bale de Chaleur a f t e r the area outside i s c l e a r , i t i s usually confined to the southern s i d e . Northumberland S t r a i t c l e a r s from west to east and the east coast of Prince Edward Island tends to open e a r l i e r than i t s surroundings. S i m i l a r l y , the area immediately east of the Magdalen Islands frequently opens e a r l y . Chedabucto Bay and the south coast of Cape Breton are encroached upon by Ice o c c a s i o n a l l y only. Although these general features of the breakup are c h a r a c t e r i s t i c of most seasons, i t i s p o s s i b l e to d i f f e r e n t i a t e the seasons on the b a s i s of s e v e r a l recurrent patterns and rates of withdrawal. The t h i r t e e n seasons may be d i v i d e d roughly Into two c a t e g o r i e s , with two exceptions. The f i r s t group comprises the years 1940, 1941, 1945, 1947, 1948, and I949. During these seasons the ice d r i f t e d from west to east and vacated the southern part of the g u l f i n a normal course of w i t h drawal. The Bale de Chaleur, Northumberland S t r a i t , George Bay, and the S t r a i t of Canso were c l e a r before the d i s p e r s a l r e g i o n , and open water appeared off the coast of Prince Edward I s l a n d at an early date. G e n e r a l l y , the steamer t r a c k was not c l e a r much i n advance of the southern r e g i o n s . In a l l but the two seasons of 1940 and 1949, some i c e along the west coast of Cape Breton was slow i n rounding Gape North, but the delay was not lengthy. A l s o , i n the case of 1941 and 1947, the i c e l i n g e r e d unduly l a t e i n the region north of the steamer t r a c k . Otherwise, the breakups followed a reasonably consistent p a t t e r n . 66 The rate of c l e a r i n g was f a i r l y r a p i d throughout both March and A p r i l during these seasons. Of course, the amount of i c e present was a d e c i d i n g f a c t o r i n determining the date of i t s complete disappearance. For example, i n 19^5> the g u l f was p r a c t i c a l l y c l e a r by the f i r s t of A p r i l , while i n 19^7, i t was not c l e a r u n t i l e a r l y May. In s p i t e of t h i s , the actual rates of breakup were comparable. The breakup of 194-2 d i f f e r e d s l i g h t l y from t h e , r e s t i n that i t progressed r a p i d l y u n t i l the end of A p r i l , then the i c e l i n g e r e d on the west coast of Gape Breton. The movement of the i c e i n these years was reasonably d i r e c t and at a r a p i d pace, without stagnating i n the southern p a r t of the g u l f . The second group includes the i c e seasons of 19^2, 1944, 194-6, 1950, and 1952, which witnessed such.stagnation as f a i l e d to occur i n the years discussed p r e v i o u s l y . Ice remained along the west coast of Cape Breton u n t i l exception a l l y l a t e dates. In most cases, the c l e a r i n g progressed u n t i l a l l but the southeastern s e c t i o n of the g u l f was free of i c e , then the process of c l e a r i n g slowed and the ice appeared to stagnate. Although the steamer track was frequently c l e a r i n advance of the southern areas, ice from the n o r t h was t h r u s t southward across the route i n 1942 and 1 9 5 ° , h i n d e r i n g n a v i g a t i o n u n t i l a f t e r the middle of A p r i l . As a r u l e , the flow of i c e through Gabot S t r a i t was r e s t r i c t e d i n A p r i l , l e a v i n g the s t r a i t p a r t l y open. U s u a l l y , Northumberland S t r a i t opened before George Bay, but i n 1952 i t was the l a s t place to c l e a r . The east coast of P r i n c e Edward I s l a n d g e n e r a l l y c l e a r e d before the Cape Breton side of the s t r a i t , but i n 1946 i t was blocked l a t e In A p r i l a f t e r being c l e a r most of the month. On the other hand, the north coast of the i s l a n d was slow In c l e a r i n g , except i n 1944. T h i s season d i s p l a y e d some of the c h a r a c t e r i s t i c s of the f i r s t group, however, i t d i f f e r e d from them p a r t i c u l a r l y i n i t s rate of breakup. In respect to r a t e s of breakup, the ice i n these years became s l u g g i s h toward the end of the season. Rapid c l e a r i n g d u r i n g March followed by gradual withdrawal i n A p r i l was the experience of the seasons of 1944 and 1946. A s i m i l a r rate of c l e a r i n g p r e v a i l e d i n 1942 and i n 1950, except that the r a t e was not so swift i n March. The 1952 season d i f f e r e d i n the fact that the withdrawal was slow i n both months. The i c e seasons i n t h i s second group, t h e r e f o r e , were c h a r a c t e r i z e d by an e a r l y spurt of c l e a r i n g fol lowed by a p e r i o d of - stagnation and accumulation of the i c e i n the southeastern s e c t i o n of the g u l f . The route v i a the S t r a i t of Canso and George Bay was blocked u n t i l long a f t e r the steamer t r a c k was open. The two years which were not included i n e i t h e r of these groups f o l l o w quite d i f f e r e n t breakup p a t t e r n s . In 1943, the i c e began c l e a r i n g i n George Bay at the south and o f f A n t i c o s t i I s l a n d i n the n o r t h . The ice i n the western p a r t of the g u l f r e t r e a t e d from both the north and south to accumulate In the c e n t r a l area. L i k e w i s e , around Cape Breton i t s h i f t e d offshore. During much of A p r i l the i c e streamed through Cabot S t r a i t , f i l l i n g i t from shore to shore. As a , r e s u l t , the steamer t r a c k was blocked u n t i l l a t e i n A p r i l , but the S t r a i t of Canso route was open remarkably e a r l y . The Bale de Ghaleur was l a t e i n c l e a r i n g . On the whole, however, the rate of breakup was swift throughout the season, e s p e c i a l l y i n view of the great quantity of ice which lay i n the g u l f that winter. The other exceptional year was 1951• In many p a r t s of the g u l f which are u s u a l l y i c e - c o v e r e d during the s p r i n g there was v i r t u a l l y no i c e . Accumulation had occurred i n the western part of the g u l f . On the outer f r i n g e s of the f i e l d s d i s p e r s a l took p l a c e , l e a d i n g to t h e i r c o n t r a c t i o n , but the main body of the i c e remained as i f pinned against the western s i d e . During the f i r s t h a l f of A p r i l the i c e moved south and f i n a l l y d i s i n t e g r a t e d before the end of the month. Because the c l e a r i n g proceeded gradually the eastern areas were not invaded by l a r g e f i e l d s dangerous to n a v i g a t i o n , but r a t h e r , remained open throughout the breakup. The rate of c l e a r i n g was slow during both March and A p r i l . These c o n d i t i o n s which p r e v a i l e d i n I95I were d e f i n i t e l y remarkable, i f not unique. THE DETERMINING FACTORS OF THE BREAKUP The behaviour of the i c e i n a l l phases of i t s formation and breakup i s c o n t r o l l e d by the p h y s i c a l f a c t o r s of the environment. Many of these f a c t o r s were i n d i c a t e d p r e v i o u s l y , but i t i s necessary to re-examine them i n the l i g h t of an understanding of the i c e c o n d i t i o n s . The aim of t h i s d i s c u s s i o n s h a l l be to determine the r e l a t i v e influence of each f a c t o r . The Non-Variable Factors The influence of some of these f a c t o r s does not vary appreciably from year to year; for^ t h i s reason they may be termed n o n - v a r i a b l e . Those which are discussed are the s u b a e r i a l and submarine morphology, the t i d e s and t i d a l c u r r e n t s , and the ocean c u r r e n t s . S u b a e r i a l and Submarine Morphology Because i c e formation takes place more r e a d i l y where the water i s shallow, l o c a l ice i s more l i k e l y to o r i g i n a t e i n the southern part of the g u l f than elsewhere. Whether or not i c e forms i n great quantity i n the open g u l f i s unknown, although i t i s suspected that i t does n o t . The bays and harbours throughout the g u l f do freeze over during the w i n t e r , i f only f o r a short t ime. Where the bays are broad and shallow, as In t h i s southern r e g i o n , a great quantity of i c e i s produced. Among the bays which freeze are the Bale de Chaleur, Miramlchi Bay, and Gaspe Bay. In the wide-mouthed bays, such as George Bay, i t i s p o s s i b l e that some ice formed i n other areas f inds i t s way i n t o the bays and i s cemented i n t o a s o l i d sheet before l o c a l i c e covers them. Other regions of l o c a l ice formation are the shallows i n Northumberland S t r a i t and around the Magdalen I s l a n d s . 70 The g u l f i a so shaped that the southern p a r t acts as a b a s i n of accumulation i n t o which i c e i s d i v e r t e d as i t moves from west to east. I f Gape Breton I s l a n d were removed, the g u l f would become I c e - f r e e much e a r l i e r than i t does because i t i s the r e l a t i v e narrowness of the o u t l e t which retards the c l e a r i n g . The i c e tends to p i l e up along the west coast of Cape Breton and l i t t l e can escape through the c o n s t r i c t e d S t r a i t of Canso. The S t r a i t of B e l l e I s l e i s a l s o narrow and, i n a d d i t i o n , other forces discourage the mass movement of i c e toward t h i s opening. On the other hand, condit ions would be f a r worse i f Cabot S t r a i t were as narrow as e i t h e r the S t r a i t of B e l l e I s l e or the S t r a i t of Canso. I t s existence makes p o s s i b l e the withdrawal of most of the Ice to d i s s i p a t e i n the open A t l a n t i c , otherwise, the ice would remain i n the g u l f u n t i l i t melted. Within the main southern b a s i n are smaller bays and bights which tend to d e t a i n the i c e . There i s the bight of the north coast of Prince Edward I s l a n d where the Ice i s c r a d l e d throughout the winter. Again, there i s George, Bay whieh serves as an overflow b a s i n f o r ice i n Northumberland S t r a i t even a f t e r the bay has c l e a r e d . In t u r n , George Bay often funnels i c e i n t o the S t r a i t of Canso. And f i n a l l y , there i s the Bale de Ghaleur which always c l e a r s f i r s t along the northern s i d e , mainly because the mouth on the southern side Is obstructed by Shippigan and Miscou i s l a n d s . The Magdalen I s l a n d s , the B i r d Rocks, and B r i o n I s l a n d c o n s t i t u t e obstacles i n the path of i c e movement by s p l i t t i n g 71 the l a r g e r sheets of i c e which move toward Cabot S t r a i t . A n t i c o s t i I s l a n d serves as a p a r t i t i o n separating the i c e which o r i g i n a t e s i n t h e . S t . Lawrence River from that which comes from the northeast arm. Most of t h i s ice from the r i v e r d r i f t s along the Gaspe coast and reaches the g u l f without s u f f e r i n g detainment because the coast Is smooth. During seasons when the i c e moves southward Prince Edward I s l a n d p r o t e c t s Northumberland S t r a i t with the r e s u l t that the s t r a i t opens e a r l i e r than other southern r e g i o n s . The c o n t r o l l i n g Influence of the l a n d obviously determines the boundaries w i t h i n which the ice may move and i n d i c a t e s the routes by which the i c e may withdraw. It provides a framework which i s n o n - v a r i a b l e i n i t s f u n c t i o n . Within t h i s framework other forces a f f e c t the behaviour of the i c e . Tides and T i d a l Currents One of these forces i s the t i d a l f o r c e , with i t s a s s o c i a t e d t i d a l c u r r e n t . The disturbance of the water i s the most important inf luence exerted by the t i d a l u n d u l a t i o n , while the t i d a l currents s h i f t the i c e back and f o r t h and are r e s p o n s i b l e f o r a c e r t a i n amount of mass movement. Landfast ice which forms along shores and over shoals Is frequently shattered by the t i d a l swel l and i s c a r r i e d offshore by t i d a l currents or winds as pack i c e . This occurs commonly i n the e a r l y . w i n t e r , e s p e c i a l l y where the range of t i d e i s great. The St. Lawrence estuary, with i t s h i g h range of t i d e , must he the source of large q u a n t i t i e s of i c e because the t i d e s and currents disengage and carry away the i c e as fast as i t i s produced. This ef fect i s not so pronounced i n the v i c i n i t y of the Magdalen Islands due to the small range of t i d e here. In Northumberland S t r a i t the t i d a l currents are reasonably strong and the range of t i d e i s higher than In most sections of the g u l f . These forces are s u c c e s s f u l i n preventing the formation of a continuous sheet. Nevertheless, h e r e , and elsewhere i n the g u l f , narrow s t r i p s of landfast i c e e s t a b l i s h themselves along the shores. Outside the s t r i p s the ice i s kept i n motion. In the bays which do freeze over, Miramichi Bay, Bale de Ghaleur, and Gaspe Bay, among o t h e r s , the swell does not enter with effect iveness a f t e r the sheet of ice has s o l i d i f i e d . During the s p r i n g when the ice i s decaying, however, the t i d e regains i t s dominant p o s i t i o n and shatters the i c e sheets. The t i d a l currents i n the S t r a i t of Canso f l u s h out the i c e before an i c e - c o v e r o r i g i n a t e s . Transportat ion of great q u a n t i t i e s of i c e i s effected by t i d a l c u r r e n t s . When the wind blows i n the same d i r e c t i o n as the current flows, Ice may be c a r r i e d along at a high v e l o c i t y . Then, i f the wind continues i n the same d i r e c t i o n when the current i s r e v e r s e d , the v e l o c i t y may be reduced and only part of the ice w i l l r e t u r n to i t s o r i g i n a l p o s i t i o n . This type of movement occurs frequently In Northumberland S t r a i t , the S t r a i t of Canso, and other areas where t i d a l currents are reasonably strong. Considerable i c e i s ushered Into the g u l f and e x p e l l e d from It hy the t i d a l current i n the S t r a i t of B e l l e I s l e , because there appears to be a domi nant flow one way or the other f o r extended periods of time. Although the whole northeast arm of the g u l f becomes stopped up with i c e , the s t r a i t does not freeze over completely. B r i e f l y , the effect of t i d e s and t i d a l currents i n the g u l f i s to break up the i c e sheets i n t o pack i c e and to inaugurate movement of the pack. T h i s process often r e s u l t s i n the formation of great q u a n t i t i e s of i c e i n favourable areas, thereby i n c r e a s i n g the t o t a l amount of Ice. On the other hand, through a g i t a t i o n of the water the t i d e s r e t a r d the formation of Ice and prevent widespread c o n s o l i d a t i o n of sheet i c e . Ocean Currents The system of constant currents i n the g u l f i s d e f i n i t e l y a major f a c t o r i n c o n t r o l l i n g the movement of Ice. An Immense volume of i c e i s c a r r i e d i n t o the g u l f from the S t . Lawrence River by the Gaspe c u r r e n t . When the v e l o c i t y of the current i s reduced o f f the mouth of the Bale de Chaleur the i c e i s cast free from the stream and spreads out i n the southern part of the g u l f . A slower d r i f t s t i l l p r e v a i l s which c a r r i e s some ice toward the Magdalen Islands and Cabot S t r a i t . In s p i t e of t h i s c r o s s - g u l f flow, much of the i c e f i n d s i t s way i n t o the southern basin of the g u l f which eventually f i l l s up. A constant current off Cape North dismisses ice from the g u l f , but i t s power i s l a r g e l y wasted during the early winter beeause i t i s not supplied with i c e i n any great quantity u n t i l that from the west reaches Cabot S t r a i t . I f there were a current of comparable v e l o c i t y j o i n i n g the G-aspe and Cape Breton currents the ice from the r i v e r would be conducted d i r e c t l y into the A t l a n t i c , but such i s not the case. On the Newfoundland side of Cabot S t r a i t the current flows i n t o the g u l f . The general westward d r i f t along the south coast of Newfoundland and the inward flow around Gape Ray tend to r e p e l the invasion of i c e from the north and west. As a r e s u l t , these areas are frequently c l e a r throughout the season. S i m i l a r l y , the northward d r i f t and current along the west coast of Newfoundland keeps that coast open l a t e r i n the f a l l and c l e a r s i t e a r l i e r i n the s p r i n g than the area offshore. In the northern part of the g u l f the currents are i l l - d e f i n e d and of low v e l o c i t y , although there appears to be a general westx^ard movement. This d r i f t aids the spreading of ice from the northeast arm. Within the physiographic framexirork of the g u l f the constant currents and general movements f u r t h e r define the d i r e c t i o n s i n which the lee may move and i n d i c a t e the areas where the ice may stagnate. V a r i a b l e Factors The f a c t o r s t r e a t e d In t h i s s e c t i o n are c h a r a c t e r i z e d by annual v a r i a b i l i t y . The p h y s i c a l p r o p e r t i e s of the water and the meteorological f a c t o r s of temperature, p r e c i p i t a t i o n and wind are discussed. 75 P h y s i c a l P r o p e r t i e s of the Water As was pointed out p r e v i o u s l y , the surface temperatures of the water i n many p a r t s of the g u l f reach a p o i n t which i s favourable to the ice formation process, but due to other f a c t o r s i c e formation i s not as widespread as might be expected. The presence of imported i c e i n a given area w i l l have the effect of reducing surface temperatures i n that v i c i n i t y . This undoubtedly occurs i n the g u l f and may account f o r i c e f o r mation i n an area where i c e would not o r i g i n a t e otherwise. But on the whole, although surface temperatures are not w e l l known, i t i s suspected that they do not vary appreciably from y e a r to year as a r e s u l t of influences other than those which are meteorological i n nature. The surface water temperature i s r a i s e d by the same meteorological f a c t o r s which cause the breakup of the i c e . The r e l a t i o n s h i p between these f a c t o r s of water temperatures and weather condit ions i s c lose enough to permit the d i s r e g a r d of surface water temperatures i n view of the l a c k of Information. While the meteorological f a c t o r s exert t h e i r influence i n d i r e c t l y i n respect to i c e formation, they exert i t d i r e c t l y on the i c e i n the breakup. M e t e o r o l o g i c a l Factors It i s the meteorological f a c t o r s of the environment which are the main cause of annual v a r i a t i o n i n i c e con d i t i o n s . The c l i m a t e , which represents the average of the m e t e o r o l o g i c a l c o n d i t i o n s , can be j u s t l y compared only with average ice c o n d i t i o n s . Therefore, an i n v e s t i g a t i o n of the a c t u a l weather condit ions which p r e v a i l e d i n the t h i r t e e n years i s necessary i n order to determine the causes of the v a r i a t i o n i n these i c e seasons. Such an i n v e s t i g a t i o n p r o p e r l y r e q u i r e s a d e t a i l e d examination of the d a i l y synoptic charts over a four-month p e r i o d i n each of the t h i r t e e n y e a r s , together with a c a r e f u l study of the s t a t i o n records which are kept on f i l e at the M e t e o r o l o g i c a l D i v i s i o n o f f i c e s i n Toronto. This task was not undertaken i n connection with the present study. The aim of the i n v e s t i g a t i o n s that were c a r r i e d out was to e s t a b l i s h a general r e l a t i o n s h i p between i c e con d i t i o n s i n the breakup season and the main features of weather, namely, temperature, p r e c i p i t a t i o n and wind. The study was confined to the use of p u b l i s h e d s t a t i s t i c s , except i n the case of the examination of synoptic charts to determine wind d i r e c t i o n s and f o r c e s . The e f f e c t s of sunshine, c l o u d i ness, frequency of depressions or other a i r mass phenomena were not i n v e s t i g a t e d . Nevertheless, the f o l l o w i n g e v a l u a t i o n should e s t a b l i s h a general r e l a t i o n s h i p which might form the b a s i s f o r a more exhaustive and d e t a i l e d study. Temperature. The r e l a t i o n s h i p s between the mean monthly temperatures at a number of s t a t i o n s i n the Gulf of S t . Lawrence area during the i c e season and the i c e d i s t r i b u t i o n during the breakup were i n d i c a t e d f o r each year p r e v i o u s l y . Considering a l l the years examined, as a group, a d e f i n i t e r e l a t i o n s h i p can be e s t a b l i s h e d . . The f o l l o w i n g d i s c u s s i o n considers temperature i n r e l a t i o n to the p a t t e r n 77 of breakup, the rate of breakup, the time of f i n a l c l e a r i n g , and the quantity and extent of i c e . To f a c i l i t a t e comparison with the ice condit ions i t i s advantageous to divide the seasons i n t o groups on the basis of t h e i r temperature c h a r a c t e r i s t i c s (see Table I I , page gg). Four main groups can be i s o l a t e d . The f i r s t group, made up of the years 1940, 1945, 1949, I95I, and 1952, i s c h a r a c t e r i z e d by above average temperatures i n the i c e season. The second i s defined on the b a s i s of the fact that the f i r s t three months, e s s e n t i a l l y , are c o l d e r than the l a s t t h r e e , and Includes the years 1941, 1942, 1946, and I947. The t h i r d group i s Just the opposite i n that the f i r s t three months are warmer than the l a s t t h r e e . The years which have t h i s feature i n common are 1944, 194g, and 1950. F i n a l l y , the f o u r t h group has only one representative i n the year 19^3. * n t h i s case the temperatures of the i c e season were below average. Within these main groups there are s u b d i v i s i o n s which Indicate more s p e c i f i c a l l y the d i f f e r e n c e s between the years; these are defined on the accompanying t a b l e . The p a t t e r n of breakup i s reasonably independent of the i c e season temperatures. While there are two cases where the p a t t e r n of breakup i s s i m i l a r i n two years of l i k e temperature c o n d i t i o n s , namely, groups 2A and 2B, there i s no instance i n the f i r s t three main groups where a l l the years of one group witnessed the same p a t t e r n of breakup. Nor does the rate of breakup seem to be c o n t r o l l e d by temperatures In the ice season. There does not appear to be any consistent r e l a t i o n even w i t h i n subgroups, although again, i n group 2B 7«§ the same r a t e of breakup p r e v a i l e d i n each year. On the other hand, group IB i s c h a r a c t e r i z e d by two opposite rates of breakup. The time of f i n a l c l e a r i n g i s understood as r e p r e senting the time when a l l the i c e , except f o r s c a t t e r e d s t r i n g s and patches which do not c o n s t i t u t e a hlnderance to n a v i g a t i o n , has melted or departed from the g u l f . I t can only be roughly estimated because the information a v a i l a b l e w i l l not permit the determination of a c t u a l dates (see Table I I ) . The r e l a t i o n s h i p with temperature i s c l o s e r than i n the case of e i t h e r the p a t t e r n or the rate of breakup, but i t i s not c l o s e enough to e s t a b l i s h temperature as the main c o n t r o l In t h i s r e s p e c t . In spite of the fact that the year of e a r l i e s t c l e a r i n g , 19^5, had unusually high temperatures, the year 195 1 was l a t e r i n ^clearing and had even higher temperatures. However, two of the c o l d e r than average seasons, 1943. and 1950, were the l a t e s t i n c l e a r i n g . Low l a t e winter and early s p r i n g temperatures appear to r e t a r d the c l e a r i n g more than low f a l l and early winter temperatures. The best c o r r e l a t i o n i s discovered between the temper atures of the i c e season and the quantity and extent of i c e . 3 ^ Due to the l a c k of r e l i a b l e data concerning winter i c e c o n d i t i o n s , t h i s est imation of the s e v e r i t y pf each season i s based p r i m a r i l y on the c o n d i t i o n s e x i s t i n g i n March (see Table I I ) . The terms used to describe these c o n d i t i o n s , "quantity" i s meant the t o t a l volume of ice and by "extent" i s meant the area which i s i c e - c o v e r e d . 79 l i g h t , moderate to l i g h t , moderate, moderate to heavy, and i heavy, are r e l a t i v e only; each of the t h i r t e e n seasons i s compared with the r e s t . The term " l i g h t " i n d i c a t e s that the i c e was l e s s extensive and appeared i n smaller q u a n t i t i e s than i n the other y e a r s , while "heavy" i s taken to represent a more extensive and abundant occurrence of i c e . The other terms define intermediate c o n d i t i o n s . The seasons of h i g h temperatures coincide with those of l i g h t i c e condit ions and the seasons of low temperatures w i t h those of heavy ice c o n d i t i o n s . Between these extremes the other years f i t the p a t t e r n reasonably w e l l . I t may appear that lower temperatures i n the l a s t three months cause more severe i c e condit ions than lower temperatures i n the f i r s t t h r e e , as i s suggested i n the case of 1946 and 195° ' However, the lower temperatures may have retarded early s p r i n g c l e a r i n g which l e d to a misJudgment of the s e v e r i t y of the i c e c o n d i t i o n s . In view of t h i s p o s s i b i l i t y and c o n s i d e r i n g the nature of the Information a v a i l a b l e , the assumption Is not J u s t i f i e d . According to G. A . Mackay,25 the i c e clearance date i n Hudson Bay i s dependent mainly on the s p r i n g temperatures, and the winter temperatures have l i t t l e influence on the breakup. This a s s e r t i o n was prompted by h i s i n v e s t i g a t i o n s of a i r temperatures over Hudson Bay, p a r t i c u l a r l y at C h u r c h i l l . He was d e a l i n g mainly with landfast sheet Ice and 35Mackay, G. A . , "The E f f e c t of P r o t r a c t e d Spring Thaws on Ice Conditions i n Hudson Bay," B u l l e t i n of the American M e t e o r o l o g i c a l Society, 33: 106, March, 195 2 ' go not with s h i f t i n g pack i c e . Conditions i n the Gulf of St . Lawrence d i f f e r from those i n Hudson Bay i n s e v e r a l r e s p e c t s . A good p o r t i o n of the i c e i n the g u l f does not remain where i t i s formed, consequently, the amount of i c e present may vary considerably according to the temperatures In the season when i c e i s forming i n the producing areas. Most o f . t h e ice i s constantly s h i f t i n g pack i c e which does not remain i n the g u l f u n t i l temperatures are r a i s e d s u f f i c i e n t l y to melt i t , but r a t h e r , i t moves toward Gabot S t r a i t and i s e x p e l l e d to the open A t l a n t i c . Although the breakup of bays and harbours In the g u l f may be a c c e l e r a t e d by s p r i n g thaws, the c l e a r i n g of the g u l f as a whole may or may not respond to t h i s impetus. In 19^3, low spring temperatures may have retarded the opening of the Bale de. Chaleur, but d i d not affect the speedy withdrawal of \ the i c e from the g u l f . Then i n I 9 5 I and 1952, h i g h spring temperatures were not successful In b r i n g i n g about early withdrawal. George Bay which g e n e r a l l y freezes over com p l e t e l y Is subject to Invasions of i c e long a f t e r i t s o r i g i n a l i c e sheet has disappeared. In 194-3, however, George Bay was c l e a r more than a month before the Bale de Chaleur, i n spite , of the low s p r i n g temperatures. The smaller bays and harbours i n the g u l f were not Investigated. The conclusion i n regard to. the importance of s p r i n g thaws as a p p l i e d to the condit ions i n the Gulf of St . Lawrence must be that t h e i r primary effect i s i n decaying and breaking up i c e sheets and i n c o n t r i b u t i n g to the c l e a r i n g p r o c e s s . As a f a c t o r i n c l e a r i n g , however, s p r i n g thaws are not predominant outside the small hays. On the other hand, the winter temperatures do influence the breakup i n that they are p a r t l y responsible f o r the quantity and extent of i c e to be c l e a r e d away. The a i r temperature i s d e f i n i t e l y of fundamental . importance i n respect to i c e c o n d i t i o n s . It i s the c o o l i n g of the atmosphere, i n t u r n c o o l i n g the water, which produces i c e i n the f i r s t p l a c e . On the average, mean monthly temper atures are below f r e e z i n g f o r four months of the year, p r o v i d i n g a s u i t a b l e climate f o r i c e formation. A i r temperature i s such a v a r i a b l e f a c t o r that the temperatures of one i c e season may be quite d i f f e r e n t from those of another. These d i f f e r e n c e s are r e f l e c t e d p r i m a r i l y i n the amount and the extent of i c e which e x i s t s i n the g u l f during that season. When mean monthly temperatures are above average the ice w i l l be l e s s abundant and w i l l cover a smaller area than when temperatures are below average. In s p r i n g the h i g h e r temper atures cause melting of i c e and the breaking up of large i c e sheets i n t o pack Ice. Temperature does not appear, however, to be the most important f a c t o r determining the movements of the i c e , the rate of withdrawal, or the time of f i n a l c l e a r i n g P r e c i p i t a t i o n . An examination of the f i g u r e s f o r the d i f f e r e n c e from average of the mean monthly p r e c i p i t a t i o n and the monthly t o t a l of snowfall i n inches suggests that the inf luence of p r e c i p i t a t i o n on i c e c o n d i t i o n s In the g u l f i s 82 sl ight.26 i n t h i s i n v e s t i g a t i o n the same s t a t i o n s were used as i n the case of temperature. The main effect of p r e c i p i t a t i o n seems to be the r e t a r d a t i o n of f r e e z i n g by a snow-cover. A heavy blanket of snow l y i n g on the ice throughout the winter months helps to r e t a i n heat. This l i m i t s the thickness of the i c e because i t i s c h i e f l y through conduction of heat upward that the i c e sheet i s able to b u i l d downward on the under s i d e . In those years when the i c e was heavy, as i n 1943, 1948, and 1950, the tendency was toward lower than average snowfalls . On the other hand, when the i c e was l i g h t e r , as i n 1945 and 1946, the tendency was toward higher than average snowfalls. ' The c o r r e l a t i o n i s by no means c l o s e , however. Whether or not t h i s influence i s important, heavy snowfall i s responsible f o r the formation of s l u s h . When low temperatures f o l l o w a snowfall the s l u s h frequently provides a mortar which aids i n cementing pack i c e i n t o l a r g e sheets. During the breakup the effect of p r e c i p i t a t i o n i s r e l a t i v e l y i n s i g n i f i c a n t . Throughout the ice season, as a whole, It i s l i k e l y that p r e c i p i t a t i o n performs a minor r o l e i n determining the ice condit ions i n the g u l f . Wind. The wind i s d e f i n i t e l y the most important f a c t o r i n determining the d e v i a t i o n from the expected p a t t e r n and rate of withdrawal of the ice as d i c t a t e d by the non- 3°Department of Transport, Meteorological D i v i s i o n , Monthly Record (monthly s t a t i s t i c s s e r i e s ) . Toronto, 1940- 1950. S3 v a r i a b l e f a c t o r s . As was i n d i c a t e d by the wind roses ( f o l l o w i n g page 27), p r e v a i l i n g winds throughout the winter and s p r i n g have a westerly component, but i n s p r i n g t h i s domi nance i s l e s s pronounced. Although the d r i f t of f l o a t i n g i c e i s approximately t h i r t y degrees to the r i g h t of the wind d i r e c t i o n , due to the e a r t h ' s r o t a t i o n , i t v a r i e s according to the closeness of the pack. In any case, i t i s p o s s i b l e to deal with the effect of wind i n the general terms, n o r t h e r l y , e a s t e r l y , southerly , and westerly without s p e c i f y i n g a c t u a l d i r e c t i o n s . There i s no doubt that westerly winds are a potent f a c t o r , combining with the c u r r e n t s , i n causing the i c e to move toward Cabot S t r a i t . In order to d i s c o v e r the inf luence on the i c e of the annual v a r i a t i o n of the wind, the s t a t i s t i c s f o r the t o t a l mileage of wind by d i r e c t i o n s were examined at twelve s t a t i o n s . 37 These f i g u r e s i n d i c a t e the p r e v a i l i n g d i r e c t i o n f o r each month as determined by the t o t a l v e l o c i t y of the wind, rather, than by the t o t a l hours of wind. In a d d i t i o n , d a i l y synoptic charts f o r the months of March and A p r i l were scanned i n the case of the years 1944, 1945, 1945, 1951, and 1952. These observations proved that the winds d u r i n g February, March, and A p r i l are the primary c o n t r o l of the p a t t e r n and rate of breakup, as w e l l as of the time of f i n a l c l e a r i n g . A short p e r i o d of strong wind from one d i r e c t i o n tends to have a greater effect on i c e movement than a l o n g p e r i o d 5 7 I b l d . . 1940-1950. of weak wind. This i s l o g i c a l because the wind must overcome the forces of f r i c t i o n before the i c e can be moved appreciably. Therefore, gales exert an influence q u i t e out of p r o p o r t i o n to the length of time they blow. Strong winds are able to over power water currents i n some i n s t a n c e s . Only the constant currents i n the g u l f are never checked by the wind; the weak flows and the t i d a l currents are a l l susceptible to the power of wind, e s p e c i a l l y when loose i c e i s present. The i c e f l o e s present the wind with a rougher surface that i s e a s i e r to g r i p . Not only does the wind a i d or hamper the normal water current flow, but a l s o i t generates currents which may continue to flow even a f t e r the wind has abated. In view of the great t r a n s p o r t i n g power of wind, i t i s obvious that a p e r i o d of several days with sustained strong wind from one d i r e c t i o n can r e d i s t r i b u t e tremendous q u a n t i t i e s of pack i c e i n the g u l f . The frequency of such periods of wind from the same d i r e c t i o n d u r i n g February, March, and A p r i l i s of utmost importance. For example, . in 1952, strong n o r t h e r l y winds p r e v a i l e d f o r several periods of a week or more i n February and March, r e s u l t i n g i n accumulation of the i c e i n the southern part of the g u l f (see Table I I , page &9). The same process occurred i n 1951, except that the winds were more e a s t e r l y and continued u n t i l the middle of A p r i l , d r i v i n g the lee toward the western s e c t i o n . In 1943, sustained southerly winds were responsible f o r pushing the i c e northward where i t found i t s way out of the g u l f r e a d i l y . These cases are extreme; the more l i k e l y occurrence i s the c a n c e l l i n g of the work of one p e r i o d by that of another. That i s to say, i f the winds are strong e a s t e r l y f o r a few days, they may be strong westerly i n the next p e r i o d . Often the periods are short and cause only minor d i v e r s i o n s of the i c e . A p e r i o d of very l i g h t v a r i a b l e winds may create a stagnation of the ice as occurred i n l a t e A p r i l , 1952. These influences of the wind are r e f l e c t e d , as has been pointed out, i n the pattern of breakup. Those years i n which the i c e tended to stagnate i n the southern part of the g u l f were c h a r a c t e r i z e d by excessive strong n o r t h e r l y wind at some time d u r i n g the season or l a c k of s u f f i c i e n t southerly wind. In some cases there was an a c t u a l accumulation of ice i n the south, as i n 1 9 5 2 , while i n others the i c e present simply d i d not withdraw r e a d i l y , as i n 19^4. The season of 1952 serves as an example of stagnation throughout A p r i l due to weak and v a r i a b l e winds as w e l l as one of southern . accumulation. On the other hand, the years i n which the i c e withdrew more r e a d i l y from west to east experienced a favourable combination of wind throughout the s p r i n g season. Short periods of southerly winds followed by longer periods of westerly appear to assure the withdrawal of the i c e from the south. I f strong winds occur f r e q u e n t l y , as In 19^5* the exodus i s a c c e l e r a t e d . The other p a t t e r n s , that of 19^3, when the ice moved northward during A p r i l , and that of 1 9 5 1 , when the ice l i n g e r e d i n the western part of the g u l f , were caused by southerly and e a s t e r l y winds r e s p e c t i v e l y . &6 The influence of the wind on the rate of breakup i s apparent because the wind i s a v i t a l f a c t o r i n moving the i c e . . Should the wind combine forces w i t h the water currents i n d r i v i n g i c e through Gabot S t r a i t and i n feeding t h i s . s t r e a m with ice from the bays and bights of the more confined sections of the g u l f , the c l e a r i n g would progress r a p i d l y . But on the c o n t r a r y , should the wind oppose the water currents and other forces tending to c l e a r the g u l f , the c l e a r i n g would be r e t a r d e d . This adverse effect occurs most severely with n o r t h east winds which, c o n s i d e r i n g the d e v i a t i o n i n the d r i f t of the i c e , d r i v e the i c e southward. The case of 1952 i s witness to t h i s e f f e c t . Of course, the rate of breakup may be r a p i d through part of the season and then be slowed by n o r t h e r l y or e a s t e r l y winds f o r a short p e r i o d of time. The season of l$k-& was subject to north and northeast winds of a h i g h v e l o c i t y toward the end of A p r i l which forced the ice onshore along the east coast of Cape Breton, although i t had been offshore throughout most of the month. S i m i l a r l y , the time of f i n a l c l e a r i n g i s mainly determined by the wind. In r e t a r d i n g the withdrawal of i c e by causing stagnation i n the southern s e c t i o n , the wind i s d i r e c t l y responsible f o r i c e remaining unduly l a t e i n the g u l f . In several instances when there was a d i r e c t withdrawal, the i c e was h e l d onshore i n the d i s p e r s a l region by e a s t e r l y winds. The quantity and extent of i c e are also affected by the wind. When ice formation i s i n progress the wind aids the t i d e s and t i d a l currents i n disengaging i c e from the l a n d 87 and from shoals i n the producing areas and c a r r y i n g i t away to add to the s h i f t i n g pack. The extent of i c e may he reduced m a t e r i a l l y by accumulation i n one p a r t i c u l a r area as a r e s u l t of wind. In t h i s manner the wind i s often responsible f o r the closeness of pack i c e . Most of the s h i f t i n g i n p o s i t i o n of pack Ice i s caused d i r e c t l y by the wind. Northerly winds brought i c e southward b l o c k i n g the steamer t r a c k i n m i d - A p r i l i n the seasons of 1942 and I95O. In 1948, southerly winds pushed the ice to the north side of Northumberland S t r a i t about the middle of A p r i l and kept the i c e off the Gape Breton east coast. Likewise, i n I952, the i c e was s h i f t e d from one side of the s t r a i t to the other around A p r i l 25. Westerly winds general ly c l e a r southeast c o a s t a l areas r e a d i l y . T h i s effect may be n o t i c e d along the n o r t h side of the Bale de Chaleur, the southeast coasts of Prince Edward I s l a n d , the Magdalen I s l a n d s , and Cape Breton I s l a n d . The northward movement of i c e i n 19^3> occasioned by southerly winds, e f f e c t i v e l y blocked the mouth of the Bale de Chaleur which greatly retarded i t s c l e a r i n g . The wind i s of.utmost Importance i n the c l e a r i n g of i c e from the g u l f . On the average, the p r e v a i l i n g westerly winds during the ice season assure that most of the ice w i l l eventually depart from the g u l f through Cabot S t r a i t . The l o s s of dominance by westerly winds f o r varying periods of time r e s u l t s i n a d i f f e r e n t behaviour of the i c e . Periods of sustained n o r t h e r l y o r e a s t e r l y winds cause accumulation of i c e i n the southern part of the g u l f and slow the rate of . SABLE II BJSLAIIONSHIPS BETWEEN TEMPEHATOEE, WIND, AND ICE CONDITIONS gg Group Temperatures Year Winds Pattern of Breakup Bate of Breakup Time of Final Clearing Quantity and Extent of Ice • j (. . . . . . . . . . . . . . . . . . rapid i n March and i p r i l early i p r i l l i g h t 1. above average temperatures A. every month well above average 19^ 5 strong westerly west to east, direct withdrawal 195I strong easterly and northerly west side accumulation slow in March 'and i p r i l late i p r i l light B.: ( most months well above average 1949 northerly and westerly west to east, direct withdrawal rapid i n March and .April late April moderate to light stagnation i n south moderate to light 1952 strong northerly and light, variable slow i n March and April early May c. most months (insufficient data)" west to east, direct withdrawal above average or near average 19*40 moderate in March, rapid i n i p r i l early May moderate to light - A. f i r s t three months near average, last three months higher than average 1942 strong northerly stagnation In south moderate i n March, slow i n i p r l l early May moderate to light 2. f i r s t 3 mouths colder than last 3 1946 strong westerly followed by northerly and easterly stagnation i n south rapid in March slow i n i p r l l early May moderate - B.: f i r s t three months /; lower than average; last three higher than average 1 9 ul (insufficient data) west to east, direct withdrawal rapid i n March and i p r l l late i p r i l moderate to heavy 1947 westerly and southerly west to east, direct withdrawal rapid i n March and i p r l l early May moderate to heavy i - 3. f i r s t 3 months warmer than last 3 A . ; f i r s t three months above average, last three months below, average l9*+g strong westerly followed by strong northerly and easterly west toceast, direct withdrawal rapid i n March and i p r i l middle of May heavy moderate in March slow i n i p r i l middle of May heavy 1950 strong northerly stagnation in south Two of f i r s t three 19I& moderate to heavy B.J months above average last three below average strong westerly and northerly stagnation i n south rapid i n March slow i n i p r i l late i p r i l ; k four months well below average 1943 rapid in March and i p r i l early May heavy "below average temperatures strong southerly and westerly south to north, direct withdrawal c l e a r i n g . Westerly and southerly winds i n combination l e a d to the prompt withdrawal of i c e through Gabot S t r a i t . As a r e s u l t , wind i s the major f a c t o r in/determining the pattern and rate of breakup as w e l l as the time of f i n a l c l e a r i n g , and i t i s responsible f o r many of the minor changes i n p o s i t i o n of the pack i c e . SUMMARY The process of i c e formation and melting i s d i r e c t l y caused by temperature. Because data i s l a c k i n g concerning water temperatures, only a i r temperatures are used as an Index of the inf luence of t h i s f a c t o r . The f a c t that the temper atures do become low enough i n winter to cause formation of i c e and h i g h enough i n s p r i n g to cause melting e s t a b l i s h e s temperature as the primary f a c t o r i n determining i c e con d i t i o n s . Beyond the bounds of average c o n d i t i o n s , annual v a r i a t i o n s of temperature l a r g e l y determine the quantity and extent of i c e and to a c e r t a i n degree the time of f i n a l c l e a r i n g . With the temperature favourable to i c e formation, i t i s p a r t l y the shallowness of some areas that Induces ioe to o r i g i n a t e and i t i s the physiographic framework which Is responsible f o r o b s t r u c t i n g the free movement of i c e to the open ocean. The bays and bights d e t a i n the ice and offshore i s l a n d s c o n s t i t u t e obstacles In the path of movement. Assuming the existence of i c e w i t h i n t h i s framework, the f a c t o r s of movement exert t h e i r i n f l u e n c e . The t i d e s are e f f e c t i v e i n breaking i c e sheets which have formed along the shore o r - o v e r shoals and winds and t i d a l currents keep the i c e i n motion i n many sections of the g u l f throughout the winter. In t h i s manner the t o t a l i c e supply i s augmented. Constant ocean currents provide a system of t r a n s p o r t a t i o n which c a r r i e s i c e i n t o the g u l f from the St. Lawrence estuary and also conducts ice outside through Cabot S t r a i t . The l a c k of constant currents i n the southern part of the g u l f to a i d i n the removal of ice i s p a r t l y responsible f o r the s t a g nations which frequently occur In that a r e a . But these f a c t o r s of movement cannot e x p l a i n the remarkable v a r i e t y of behaviour patterns of the i c e . I n s t r u mental i n causing these v a r i a t i o n s i s the wind. It appears to be the predominant f a c t o r i n determining the p a t t e r n and r a t e of breakup and, to a c e r t a i n degree, the time of f i n a l c l e a r i n g and the quantity and extent of i c e . The c o n t i n u a l f l u c t u a t i o n of pack i c e i n r e l a t i o n to the l a n d i s e s s e n t i a l l y due to the wind's Influence. While there are numerous other f a c t o r s which influence the ice d u r i n g the breakup season, i t - i s suggested that these are the major ones. CHAPTER VI CONCLUSION The I n v e s t i g a t i o n of the d i s t r i b u t i o n of i c e i n the Gulf of St . Lawrence during t h i r t e e n breakup seasons y i e l d s the f a c t that the behaviour of the i c e i s extremely v a r i a b l e , although i t follows c e r t a i n p a t t e r n s . Examination of e n v i r o n mental f a c t o r s which exert an influence on the i c e reveals d i s t i n c t c o r r e l a t i o n s with the behaviour of the i c e . These f a c t o r s , both n o n - v a r i a b l e and v a r i a b l e i n f u n c t i o n , act i n combination to determine the i c e behaviour, but i t Is the v a r i a b l e f a c t o r s , mainly m e t e o r o l o g i c a l , which are c h i e f l y responsible f o r the year to year d i f f e r e n c e s . In view of the v a r i a b l e behaviour of the i c e due to these f a c t o r s , the determination of average condit ions i s rendered d i f f i c u l t . The t h i r t e e n - y e a r p e r i o d examined i s hardly long enough to achieve v a l i d averages. It i s e s t a b l i s h e d that many of these years were d i s t i n c t l y above average i n respect to temperature, while few were below average. This fact serves to Indicate that the i c e condit ions of t h i s p e r i o d , as a whole, were l e s s severe than those which might be expected i n a future p e r i o d . Nevertheless, c e r t a i n g e n e r a l i z a t i o n s can be made with j u s t i f i c a t i o n . The Gulf of S t . Lawrence i s never completely I c e - covered; there are always areas of open water because much of the i c e i s s h i f t i n g pack i c e , e s p e c i a l l y i n the c e n t r a l . p a r t . The southern s e c t i o n Is an area of accumulation and there are u s u a l l y l a r g e Ice sheets i n t h i s r e g i o n as w e l l as c o n s i d e r able close pack i c e . In most parts of the g u l f the ice does not remain i n the spring u n t i l It m e l t s , but r a t h e r , i t d r i f t s i n t o the open A t l a n t i c p r i m a r i l y through Cabot S t r a i t . The discharge of i c e i s commonly i n progress during February, but i t i s a c c e l e r a t e d i n March. Cabot S t r a i t i s seldom completely blocked f o r more than a few days at a t ime, In s p i t e of the statement which appears i n the G-ulf of S t . Lawrence P l l o t ^ to the effect that i t i s blocked s o l i d with i c e nearly every year, often f o r three weeks at a time. The i c e f i e l d i n the d i s p e r s a l region general ly extends eastward past 5& degrees west and southward past 45 degrees n o r t h . O c c a s i o n a l l y , the ice moves onshore along the south coast of Cape Breton under the inf luence of e a s t e r l y winds, but seldom encroaches on the area o f f the south coast of Newfoundland. Most of the' i c e which i s the f i r s t to depart from the g u l f comes from the c e n t r a l area between A n t i c o s t l I s l a n d and Gabot S t r a i t . However, t h i s c e n t r a l region may continue to be i c e - c o v e r e d u n t i l l a t e i n March or early i n A p r i l due to Invasions of i c e from other areas. Most of the i c e i n the lower estuary of the St. Lawrence R i v e r f inds i t s way i n t o the g u l f by the middle of March, l e a v i n g the s t r e t c h between Pointe des Monts and the g u l f c l e a r of i c e . Toward the end of March the steamer route opens and allows n a v i g a t i o n to commence. Frequently, the passage north of - A n t i c o s t l Is land c l e a r s before that south ? Department of Mines and Resources, Gulf of St. Lawrence P i l o t , T h i r d E d i t i o n . Ottawa, 1946, p . L . of i t . The steamer t r a c k i s sometimes blocked by i c e during A p r i l when n o r t h e r l y winds d r i v e i c e from the northeast arm across i t . O r d i n a r i l y , however, the i c e north of a l i n e from Cape St . George to Natashquan i s not discharged through Cabot S t r a i t but tends to d r i f t northward where i t d i s i n t e g r a t e s and melts. E a r l y i n A p r i l the ice withdraws from the western p a r t of the g u l f , l e a v i n g i c e i n the Baie de Chaleur, although the bay i s c l e a r i n g along the northern s i d e . Throughout the southern s e c t i o n the l a r g e r ice sheets are breaking up, rendering the i c e more mobile. In the meantime, the stream of i c e through Cabot S t r a i t continues with the bulk of ice confined to the Cape Breton s i d e . The f i e l d of i c e beyond the s t r a i t has receded from i t s p o s i t i o n of greatest extent i n March. As the month progresses the i c e moves toward Cabot S t r a i t . The region around the Magdalen Islands c l e a r s before the southern area and the b e l t of Ice In Cabot S t r a i t becomes narrower. Most of the i c e has departed from the Baie de Chaleur by the end of the t h i r d week i n A p r i l . Northumberland S t r a i t c l e a r s from i t s western entrance eastward and the l a s t Ice to withdraw from the g u l f In l a t e A p r i l or e a r l y May Is that i n the southeastern sector along the west coast of Cape Breton. Sometimes the S t r a i t of Canso c l e a r s i n e a r l y A p r i l , but i t i s dependent on the c l e a r i n g of George Bay and the Ice may remain here u n t i l the end of the month. Likewise, ice i s found i n the d i s p e r s a l r e g i o n off the Cape Breton east coast u n t i l the end of A p r i l . The i c e f i e l d s are constantly s h i f t i n g p o s i t i o n . Some areas may be c l e a r at c e r t a i n times and i c e - c o v e r e d at o t h e r s , depending p r i m a r i l y on the d i r e c t i o n of the wind. Such f l u c t u a t i o n s are e s p e c i a l l y n o t i c e a b l e along the east and south coasts of Cape Breton where the ice may be d r i v e n a l t e r n a t e l y onshore and offshore by the wind. As a r e s u l t of these encroachments, Louisburg harbour i s sometimes blocked f o r a few days i n A p r i l , but usual ly there e x i s t s a shore l e a d i n s i d e the ice f i e l d . The east coast i s more s u s c e p t i b l e to these invasions because the i c e does not c l e a r from t h i s area u n t i l the end of A p r i l or e a r l y May. Consequently, Sydney harbour may be blocked f o r longer periods and u n t i l a l a t e r date than Louisburg. The v a r i a b i l i t y of the i c e condit ions i n the breakup season i s w e l l i l l u s t r a t e d by the t h i r t e e n years examined. With the g u l f e s s e n t i a l l y open by the end of March, the year 1945 probably witnessed one of the e a r l i e s t c l e a r i n g s which might be expected. On the other hand, the year 1950 saw i c e remain i n the g u l f u n t i l May 15. The unusual patterns of breakup which c h a r a c t e r i z e d the years 1943 and 195 1 m ay n^t occur f r e q u e n t l y , but I t i s p o s s i b l e that other p a t t e r n s , equally d i s t i n c t i v e , that are not represented among the years studied may yet occur. On the b a s i s of the t h i r t e e n years i t appears t h a t , most often, the i c e w i l l e i t h e r withdraw d i r e c t l y from the west to east , passing through Cabot S t r a i t r e a d i l y , or w i l l tend to stagnate i n the southern part of the g u l f toward the end of the season. BIBLIOGRAPHY BOOKS Atwood, W. W., The Physiographic Provinces of North America, Boston: Ginn and Company, 19^0 " 536 pp. Barnes, Howard T . , Ice Engineering. Montreal: Renouf P u b l i s h i n g C o . , 1928. 364 pp. Johnson, Douglas W., The New England-Acadian S h o r e l i n e . New York: John Wiley and Sons, I925. 60S pp. Johnson, Douglas W., Shore Processes and Shoreline Development. New York: John Wiley and Sons, I n c . , I9I9. Koeppe, Clarance Eugene, The Canadian Climate. Bloomlngton, I l l i n o i s : McKnight and McKnlght, 1931. 280 pp. Shepard, F r a n c i s P . , Submarine Geology. New York: Harper and B r o t h e r s , 1948. 348 pp. Stewart, John Q., Coasts. Waves and Weather. Boston: Ginn and Company, 1945. 348 pp. Sverdrup, H. U . , M. W. Johnson, and R. H . Fleming. The Oceans. New York: P r e n t i c e - H a l l , 1946. 1,087 pp. T a y l o r , G r i f f i t h , Canada. London: Methuen and C o . , 1947. 524 pp. PERIODICALS Barnes, H . T . , "St. Lawrence and I t s Ice Problems," Canadian Engineer. 57:738-39, November 19, 1929. Barnes, H. T . , "Ice Formation on the S t . Lawrence," Canadian Engineer. 20:789-92, June 8, 1911. Bencker, L i e u t .-Commander H . , "Ice Terminology," The Hydrographic Review, 8:114-31, November, 1931. Boughner, C. C , "The Climate of Canada," Quarterly Journal of the Royal Meteorological S o c i e t y . 63:419-31. jTriyT^L^TT" Gordon, A. R . , and W. C. Woodworth, "Some I n t e r - R e l a t i o n s h i p s of Snow and Ice Conditions and Weather i n the A r c t i c , " B u l l e t i n of the American M e t e o r o l o g i c a l S o c i e t y , 31:271-7s7~0cTober, I956. Hachey, H. B . , "Surface Water Temperatures of the Canadian A t l a n t i c C o a s t , 0 J o u r n a l of the F i s h e r i e s Board- of Oanada, 4 : 3 7 6 - § l , February, 1940. Hare, F . Kenneth, "The Climate of the I s l a n d of Newfoundland: A Geographical A n a l y s i s , " Geographical B u l l e t i n , 2:36-88, 1952. Hare, F . K . , and M. R. Montgomery, "Ice, Open Water, and Winter Climate i n the Eastern A r c t i c of North America," Parts 1 and 2, A r c t i c . 2:79-89, 14-9-64, September and December, 194§. K e r r y , J . G . G . , "Winter Navigation on the St . Lawrence," The Dock and Harbour A u t h o r i t y . 31:220-225, November, K e r r y , J . G . G . , "The S t . Lawrence Waterway, an A l l - C a n a d i a n and Very Deep Route," The Engineering J o u r n a l , 34:536-43, June, 1951. . K e r r y , J . G . G . , "Ice Blockade of Canadian P o r t s , " The Dock and Harbour A u t h o r i t y , 27:273-76, March, 19^7? K e r r y , J . G . G . , "The S t . Lawrence Waterway," ( d i s c u s s i o n of the paper, "The S t . Lawrenee Waterway, An A l l - Canadian and Very Deep Route"), The Engineering J o u r n a l . 34:957-65, October, 1951. Mackay, G. A . , "The E f f e c t of P r o t r a c t e d Spring Thaws on Ice Conditions i n Hudson Bay," B u l l e t i n of the American M e t e o r o l o g i c a l S o c i e t y , 33:101-O"o". March. 1952. Putnam, D. F . , "Climate of the Maritime P r o v i n c e s , " Canadian Geographical J o u r n a l , 21:135-47, September, 1940. "Sea Ice: Terminology, Formation and Movement," The P o l a r Record, 4:126-33, January, 1944. Smith, E . H . , "Some M e t e o r o l o g i c a l Aspects of the Ice P a t r o l Work i n the North A t l a n t i c , " Monthly Weather Review, 50:629-31, December, 1922. "Symposium, Canada's Oceans—Known and Unknown," Proceedings of the Royal Society of Canada, 4-3:153-90, June, 1949. 97 GOVERNMENT PUBLICATIONS Dawson, W. B e l l , The Tides and T i d a l Streams With I l l u s t r a t i v e Examples From Canadian Waters. Ottawa: Department of the Naval S e r v i c e , 1920" 4"3"~pp. Department of Marine and F i s h e r i e s , The Currents on the Southeastern Coasts of Newfoundland. Ottawa, I906. Department of Marine and F i s h e r i e s , The Currents i n B e l l e I s l e S t r a i t . Ottawa, I907. Department of Mines and Resources, G u l f of St . Lawrence P i l o t . T h i r d E d i t i o n . Ottawa, 19457 376 pp. Department of Mines and Resources, Hydrographic S e r v i c e , "General Correspondence on Ice C o n d i t i o n s , " F i l e No. 634, v o l . 3. Ottawa, I 922 - I 9 5 I . Department of Mines and Resources, Hydrographic S e r v i c e , "Daily Ice R e p o r t s , " F i l e No. 634, v o l . 2. Ottawa, 1941-1951. Department of Mines and Resources, Hydrographic S e r v i c e , "Questionnaire, Re: Ice Conditions i n the Gulf of St. Lawrence," F i l e No. 634, v o l . 1. Ottawa, 1937. Department of Mines and T e c h n i c a l Surveys, Tide Tables f o r the A t l a n t i c Coast of Canada, also Current tables and Information on Currents. Ottawa, 1952. T2b pp. Department of Mines and Technical Surveys, Tide Levels and T i d a l Bench Marks. Ottawa, 1951. 88 pp. Department of Mines and T e c h n i c a l Surveys, Geographical Branch, "Canadian Ice D i s t r i b u t i o n Survey F i l e , " Ottawa, 1951. Department of the Naval S e r v i c e , The Currents i n the Gulf of S t . Lawrence. Ottawa, 1913. 4b pp. Department of the Naval S e r v i c e , The Currents i n the Entrance to the St. Lawrence. Ottawa, 1913* 5 Q PP' Department of the Naval S e r v i c e , Temperatures and D e n s i t i e s of the Waters of Eastern Canada. Ottawa, 192~eT 102 pp. Department of Trade and Commerce, Dominion Bureau of S t a t i s t i c s , "The Climate of Canada. Part I I , " The Canada Year Book 1950. Ottawa, 1950. pp.V^3^.70. Department of Trade and Commerce, Dominion Bureau of S t a t i s t i c s , "The Climate of Canada, Part I , " The Canada Year Book 1943-49. Ottawa, 194-9. pp.TT -63. Department df Transport, "Ice Report of G.G.S. G l t a d e l l e , " F i l e No. 3262-3, v o l . 1. Ottawa, 1940. Department of Transport , "Ice Report of C.G-.S. N. B. Maclean," F i l e No. 8262-3, v o l . 1. Ottawa, 1940. Department of Transport, "Reports of A e r i a l Ice Surveys i n the Gulf of St . Lawrence," F i l e No. 8262-3, 8 v o l s . Ottawa, 1940-1952. Department of Transport, M e t e o r o l o g i c a l D i v i s i o n , C l i m a t i c Summaries f o r Selected M e t e o r o l o g i c a l S t a t i o n s i n the Dominion of Canada, 2 v o l e . Ottawa. 1948. Department of Transport, M e t e o r o l o g i c a l D i v i s i o n , Monthly Record (monthly s t a t i s t i c s s e r i e s ) . Toronto, I940-I950. Department of Transport, M e t e o r o l o g i c a l D i v i s i o n , Monthly Weather Map (monthly weather map s t a t i s t i c s s e r i e s ) . Toronto,"T951-1952. O u t s e l l , B. V . , An I n t r o d u c t i o n t o , t h e Geography of Newfoundland, Information S e r i e s No. 1. Ottawa: Department of Mines and Resources, Geographical Bureau, 1949.: 85 pp. Huntsman, A . G . , A r c t i c Ice On Our E a s t e r n Coast, B u l l e t i n No. 13, B i o l o g i c a l Board of Canada. Toronto, January, 1930. Jones, I , W., "An Outl ine of the Geology of the Province of Quebec," Province of Quebec S t a t i s t i c a l Yearbook 1947. Quebec: Government of Quebec, 19^7* PP. Kriegsmarine, Ubootshandbuch der Ostkdste Kanadas ( A t l a s ) . B e r l i n , xTpBT. pp. 166,"TfO" Sandstrdm, J . W., "The Hydrodynamics of Canadian A t l a n t i c Waters," Canadian F i s h e r i e s E x p e d i t i o n , 1914-1915. Ottawa, I919. PP. 221-91. Smith, F . C . G . , "Hydrographical F e a t u r e s , " Canada Year Book 1947. Ottawa: Department of Trade and Commerce, Dominion Bureau of S t a t i s t i c s , 1947. pp. 3-12. Soule, F l o y d M . , and E . R. Challender, "Discussion of Some of the E f f e c t s of Winds on Ice D i s t r i b u t i o n i n the V i c i n i t y of the Grand Banks and the Labrador S h e l f , 8 I n t e r n a t i o n a l Ice Observation and Ice P a t r o l Service In the North A t l a n t i c Ocean, Season of 1947. Washington: U. S. Treasury Department, Coast Guard, 19^9. PP..59-61. U . S. Navy, Hydrographic O f f i c e , Ice A t l a s of the Northern Hemisphere, F i r s t E d i t i o n . Washington, 1946T U . S. Navy, Hydrographic O f f i c e , World A t l a s of Sea Surface Temperatures. Washington, 194-8. U . S. Navy, Hydrographie O f f i c e , "A F u n c t i o n a l Glossary of Ice Terminology," Study No. 103, P r o v i s i o n a l , May, 1948. U . S. Treasury Department, Coast Guard, I n t e r n a t i o n a l lee Observation and leg P a t r o l Service i n the North A t l a n t i c " S c e a n , B u l l e t i n s 3 1 , 3 2 . 357 34, and 35. (Seasons 1941 to 1949, i n c l u s i v e ) . Washington, 1941-1949. \ —- J„.,' APPENDIX '\, 'MAPS OF 'LIMITS OF MAIN ICE AREAS 9 Season of 1940 101 Season of 1941 11 Season of 1942 12 Season of 1943 13 Season of 1944 ' 14 Season of 1945 ' 15 Season of, 1946 ' > 16 Season of I947 17 Season of 1948 18 Season of 1§49 19 Season of 1950 20 Season of I95I 21/'Season of 1952 6 4 5 0 GULF OF ST. LAWRENCE LIMITS O F M A I N I C E A R E A S BREAKUP S E A S O N OF 1 9 4 0 Ice L i m i t s . April 5 fh April IS fh April 25 th M E A N M O N T H L Y T E M P E R A T U R E D I F F E R E N C E FROM A V E R A G E (EOC N > N O V 1 9 3 9 D E C 1 9 3 9 J A N 1 9 4 0 F E B 1 9 4 0 M A R 1 9 4 0 o\ 2 41 6 S A P R 1 9 4 0 6 6 GULF OF ST. LAWRENCE L I M I T S OF M A I N ICE A R E A S B R E A K U P S E A S O N OF 1941 N O V . 1 9 4 0 D E C 1 9 4 0 J A N 1 9 4 1 F E B 1 9 4 1 M A R 1 9 4 1 A P R 1 9 4 1 GULF OF ST. LAWRENCE LIMITS OF MAIN ICE AREAS BREAKUP SEASON OF 1943 M E A N M O N T H L Y T E M P E R A T U R E D I F F E R E N C E FROM A V E R A G E N O V 19 4 2 D E C 1 9 4 2 J A N 1 9 4 3 F E B 1 9 4 3 M A R 1 9 4 3 A P R 1 9 4 3 •Ol 10 -14 S a b l e I s i o n d GULF OF ST. LAWRENCE LIMITS OF MAIN ICE AREAS BREAKUP SEASON OF 1 9 4 4 BESMB A p r . i 5 tn B H 9 A p r i l 5 ' i 6 6 6 0 5 8 4 4 M GULF OF ST. LAWRENCE LIMITS OF MAIN ICE AREAS BREAKUP SEASON OF 1945 I c e L i m i t s A p n l 5 f h A p r i l I S t h A p r i l 2 5 f h M a y I S t M a y 5 f h O p e n A o t e r A p n I 5 f h S C » L £ IN M l i E S 0 U E B E C N O D A T A M E A N MONTHLY T E M P E R A T U R E D I F F E R E N C E FROM A V E R A G E ( E a c h d o t r e p r e s e n - s o n e s t a t i o n ) N O V 1 9 4 4 ' s D E C 1 9 4 4 J A N 1 9 4 5 F E B 1 9 4 5 M A R . 1 9 4 5 A P R 1 9 4 5 So ble island H 4 6 4 4 6 2 6 0 5 8 66 GULF OF ST LAWRENCE LIMITS OF MAIN ICE AREAS BREAKUP SEASON OF 1 9 4 8 50K- 4fcr~ MEAN MONTHLY TEMPERATURE DIFFERENCE FROM AVERAGE (tad J C ' ~ n e b ' o ' i o N O V 1 9 4 7 D E C 1 9 4 7 J A N 1 9 4 8 F E B 19 4 8 M A R 1 9 4 8 HiOl 8 4 A P R 1 9 4 8 6 8 10 12 14 S c t l e i s l c r d 60 5 8 50 H 46 GULF OF ST. LAWRENCE LIMITS OF MAIN ICE AREAS BREAKUP SEASON OF 1 9 4 - 9 VEAN MONTHLY T EMPERATURE DIFFERENCE FROM AVERAGE N O V 1 9 4 8 D E C 1 9 4 8 J A N 1 9 4 9 F E B 1 9 4 9 M A R 1 9 4 9 Ssfcie i s le A P R . 1 9 4 9 be 6 6 G U L F OF ST. L A W R E N C E L I M I T S O F M A I N I C E A R E A S B R E A K U P S E A S O N O F 1951 Ice Limits A p r -1 5 th A p r i l '5 fh A p n l 2 5 frt May 1 s t May 5 '" Opei A'a'er Apnl 5 !f SC»ll IH M l t t S Q U E B E C 20 40 M A P 2 0 NO D A T A = r T E M P E RAT ORE «• . >^ • • • • i > > * •-t 4 > i - c % N O V 1 9 5 0 D E C 19 5 0 J A N 1951 F E B 1 9 5 1 M A R 1 9 5 1 A P R 1 9 5 1 4 • O V 59 64

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